chemistry panel Flashcards
What are the main tubes used for chemical analysis
Red top tube: glass )no additive) or plastic (silicone coated fro clot activation)
Tiger top/serum separator tube: gel separator/clot activation
Green top tube: lithium heparin
How do you use a red top or serum separator for a chem panel
Blood is collected and allowed to clot for 20-30 minutes (depending on presence or absence of clot activator) and centrifuged for 10 minutes at 2000-3000 rpm to obtain SERUM
If testing can not be performed within 1 hour, aliquot serum into a sterile, labelled red top tube and refrigerate/freeze to preserve
How would you use a green top tube for a chem panel
After collection, mix well and centrifuge immediately to obtain plasma
If unable to centrifuge within 1 hour, refrigerate the sample
For best results, remove plasma from cells before testing or sending out the sample
Transfer plasma to a labelled red top tube
What factors can affect chem results
hemolysis
lipemia
icterus
How does hemolysis happen and what is is
Occurs when blood is mixed too vigorously, a small gauge needle is used, or excess alcohol is applied to the skin of the patient
Intracellular fluid from the ruptured cells will dilute the sample
Intracellular components from ruptured cells may cause artificial increases in potassium, bilirubin and some enzymes including lipase
What is lipema in blood
Occurs when a patient is not fasted, and in some disease conditions
It may be difficult to obtain results on an undiluted sample
Increased risk of hemolysis
When does icterus in blood occur
Occurs when a patient has an excess of bilirubin in the peripheral blood
Results in a falsely decreased creatinine, cholesterol and total protein measurement
How soon should you run a chem panel after taking blood
Ideally all chemistry samples should be tested within 1 hour of collection
What do you do if you are not immediately using the blood for a chem panel
Remove serum/plasma from cells for testing, shipping or storage
Store in the fridge or freeze the sample for longer term storage or transport
For referred out tests, check to see what the shipping requirements are for specific tests
Do not freeze whole blood–only serum and plasma
A fasted sample is ideal to produce the most reliable results
Samples must be labelled with the patient and owner name, date, time of collection and sample type
Proteins that are commonly evaluated are
Total protein
Albumin
Fibrinogen
Where are plasma proteins produced
The majority of the plasma proteins are produced in the liver
The immune system (reticuloendothelial tissues, lymphoid tissues, plasma cells) are also responsible for making some proteins
What are the main functions of proteins
Serve as transport of carrier molecules for many plasma constituents
Role in coagulation
Hormones
Buffers to help maintain acid-base balance
Enzymes in biochemical reactions
Maintain oncotic pressure
Role in the immune response to pathogens
Though protein assays are not considered to be liver function tests, the results are indicative of a variety of disease, especially liver, kidney potentially GI disease
What are proteins affected by
Impaired hepatic synthesis
Altered protein distribution
Altered protein breakdown or excretion
Dehydration
Overhydration
What variables can affect total proteins
Dehydration→ increased protein (hyperproteinemia)
Overhydration → decreased protein (hypoproteinemia)
What is a total protein test good for
Great overall screening test for animals with edema, ascites, diarrhea, weight loss, hepatic or renal disease, blood clotting problems
What are some ways to test total protein
Refractometer
Biuret method
How do you use a refractometer to test total protein
measures the refractive index of the sample
Refractive index is influenced by the concentration of solid particles in the plasma/serum sample. Most of the solid particles in the sample are proteins
Fast, inexpensive and accurate
What is the biuret method for testing total protein and how useful is it
measures the number of molecules in serum/plasma that contains more than three peptide bonds
Simple and accurate
Commonly used by analytic instruments in the lab
How much of the plasma doe albumin take up
Makes up 35-50% of the plasma total protein in most mammals
States of hypoproteinemia are usually due to decreased albumin levels
What is the main function of albumin
Binding to other molecules in the plasma (including medications)
Transporting molecules throughout the body
Maintaining oncotic pressure
What can cause albumin levels to drop
Diffuse liver disease can cause albumin levels to fall below the reference range due to decreased albumin production
What is a condition that can cause an increse in albumin
Dehydration
What is a condition that results in albumin decreasing
Blood loss
Overhydration
Malabsorption, malnutrition and starvation
Renal disease (protein losing nephropathy)
Gi disease (protein losing enteropathy)
Hepatic insufficiency
Exudative skin disease
What are globulins and what are the types
A complex group of proteins
Alpha globulins: synthesized in the liver, carrier molecules for other proteins including HDLs and LDLs
Beta globulins: synthesised in the liver, include proteins responsible for iron transport, heme binding, complement, fibrin formation and lysis
Gama globulins (immunoglobulins): produced in plasma cells, antibodies
IgG, IgE, IgM +/- IgD
What is total protein
ALbumin + globulin = total protein
What do you use the albumin/globulin ration to determine
A/G imbalance is often the first sign of a protein abnormality
Can detect increased or decreased albumin or globulin levels
Both can be reduced in equal proportions, as with hemorrhage–the ratio will remain unchanged in this case
What is a normal albumin/globulin ratio
The A/G ratio is usually >1.00 in dogs, horses, sheep and goats
- Albumin>Globulin
The A/G ratio is usually <1.00 in cattle, pigs and cats
- Albumin<Globulin
What is fibrinogen
The soluble protein that converts to fibrin to form the matrix of blood clots
What percent of total plasma proteins is fibrinogen
3-6%
What happens if you have decreased fibrinogen
Decreased fibrinogen, as seen with hepatic insufficiency, means that the time for clot formation is prolonged or the blood will not clot at all
When are fibrinogen levels increased
Acute inflammation in large animals
With tissue damage
What are the livers functions
Metabolism of amino acids,carbohydrates and lipids
Synthesis of albumin, cholesterol and plasma proteins (including clotting factors)
Digestion and absorption of nutrients related to bile formation
Secretion of bile and bilirubin
Breakdown and elimination of toxins and drugs
What is the primary function of the gallbladder
The gallbladder works and sits alongside the liver
It’s primary function is to store bile that is produced by the liver
Pathology affecting the liver or gallbladder may result in:
Jaundice
Clotting issues
Hypoalbuminemia
Hypoglycemia
Hyperlipoproteinemia
Hepatoencephalopathy
Hepatobiliary assays is tested how
There is no single test that can be performed to fully evaluate the liver
Diseases of the liver tend to be fairly advanced by the time that they are clinically apparent
There are over 100 tests to evaluate the liver
What are some test used to evaluate the liver measures
Levels of molecules that the liver produces and metabolizes
- Bile acids–hepatic function test
- Bilirubin–hepatic function test
Molecules that are released when hepatic cells are damaged or with cholestasis (impaired flow of bile)
- The major enzymes released from damaged hepatocytes are ALT, AST, ID, GLDH
- Enzymes associated with cholestasis are ALP and GGT
Bilirubin is and produced where
Macrophages in the spleen break down hemoglobin→ insoluble bilirubin molecules are released in this process
Albumin binds to bilirubin and transports it to the liver
Hepatic cells metabolize bilirubin and it conjugates (or binds to) to glucuronide → this will become a component of bile
Conjugated bilirubin passes from the liver into the intestine where bacteria convert bilirubin glucuronide to urobilinogen
Urobilnogen is broken down how
Urobilinogen is broken down further into urobilin and excreted in feces and urine, or absorbed back into the bloodstream
Prehepatic bilirubin makes up how much of total bilirubin
Prehepatic bilirubin (bound to albumin) makes up about 2/3 of the total bilirubin in serum in most animals
Unconjugated bilirubin is increased when
Unconjugated bilirubin is increased when there is an increase in RBC destruction and there are problems with transport or uptake of bilirubin into the hepatocytes
Conjugated bilirubin is increased when
Conjugated bilirubin is increased when there is obstruction of the bile ducts
What bilirubin can assays measure
Assays can measure total bilirubin (conjugated + unconjugated) as well as conjugated bilirubin or unconjugated bilirubin–this will help to determine the cause of jaundice
How are bile acids produced
Bile acids are produced from cholesterol by hepatocytes in the liver
They aid in fat absorption and regulate cholesterol levels
Bile acids pass into the intestine via the biliary system and are stored in the gallbladder (except in horses)
Most of the bile is reabsorbed by the intestine and then processed by the liver, the rest is excreted in the feces
When can serum bile acids be increased
Serum bile acids will be elevated when the hepatocytes, biliary or portal systems are impaired in conditions such as:
Chronic hepatitis (viral, bacterial or fungal)
Hepatic cirrhosis (due to disease, drugs or toxins)
Cholestasis
Portosystemic shunts (PSS)
Neoplasia
When is serum bile acids reduced
Prolonged fasting/starvation
Diarrhea
Malabsorptive diseases
When can bile acids increase in horses
Hepatobiliary disease
Decreased food intake
Is bile acids a good test to to in cattle
Bile acid testing is not a sensitive indicator of hepatic disease in cattle
Eating, and sometimes even smelling food stimulates the gallbladder to contract and release bile into the duodenum
This will result in an increase in serum bile acids
How and when to collect specimen for bile acid testing
A serum sample is collected after a 12 hour fast, a subsequent sample is collected 2 hours after a high fat meal is ingested
Horses: a single sample is collected
What enzymes are an indicator of liver damage
“Leakage enzymes” are enzyme that leak out of damaged hepatocytes
Transaminases → catalyze reactions during amino acid production → found in tissues where protein breakdown occurs
Alanine transaminase (ALT)
Aspartate transaminase (AST)
Dehydrogenases → catalyze the transfer of hydrogen during glycolysis
Iditol dehydrogenase (ID)
Glutamate dehydrogenase (GLDH)
Alanine transferase (ALT) is and increased when
ALT is considered to be a liver specific screening test in dogs and cats
When liver is damaged, increased ALT levels are seen within 12 hours, will peak at 24-48 hours and will return to noral within a few weeks
For horses, ruminants, pigs and birds, the hepatocytes do not contain enough ALT to be considered “liver specific” (ID is a better test)
ALT is also found in the cells of the kidneys, pancreas heart and skeletal muscle, therefore damage to any of those organs will also result in an increase in ALT
Aspartate Transaminase (AST) is and where is it
ASt is present in cells of the liver, RBCs, heart skeletal muscle, kidneys and pancreas
Blood AST levels increase more slowly than ALT levels but return to normal within a day
Why can there be an elevated aspartate transminase
Hepatic disease
Muscle inflammation- strenuous exercise, IM injections or necrosis
Hemolysis – spontaneous or artifact → look at the sample
Can be correlated with creatinine kinase (CK) to determine if muscle inflammation is likely to be the cause of increased AST in a patient
Iditol dehydrogenase (ID) is and used when
ID is especially helpful for testing liver damage in larger species such as sheep, goats, swine, horses and cattle (as opposed to ALT)
Though ID testing is not readily available in many vet labs
ID levels rise quickly with hepatocellular damage or necrosis
This enzyme is very unstable in plasma or serum so specimens to be saved, transported or referred out must be frozen
Glutamate dehydrogenase (GLDH) is found where and elevated when
GLDH is found in the highest concentrations in the liver cells of cattle, sheep and goats
Elevated levels are indicative of liver damage or necrosis in cattle and sheep
Plasma and serum levels of some enzymes are predictable elevated in what
Cholestasis (impaired flow of bile)
Metabolic defects in the liver cells
With the use of certain medications
Due to the action of certain hormones (ex. Corticosteroids, thyroid hormones)
Alkaline phosphatase (ALP) is found in
Osteoblasts in bone
Chondroblasts in cartilage
Intestine, placenta and liver
Alkaline phosphatase (ALP) can be increased when
Increased ALP in large breed puppies is common during bone development: in older animals the bones are no longer growing, therefore increased levels of ALP can be attributed to cholestasis
Steroid induction in dogs
ALP testing is not useful in cattle and sheep
Most often used for dogs and cats
Gamma glutamyltransferase (GGT) is found where and when do you test it
The primary source of GGT is the liver in most animals
Blood GGT levels are higher in cattle, horse, sheep and goats than they are in cats and dogs
GGT is found in several other organs including renal, biliary and mammary epithelium
Elevated GGT levels are suggestive of liver disease, especially obstructive liver disease
Elevation of liver enzymes should correlate with what
Results that are associated with other organs
Correlating glucose (pancreas) and liver results
Correleting AST to CK (muscle results)
History and clinical signs
Signalment
What does the kidney do
Conserve and eliminate water and electrolytes
Conserve and eliminate hydrogen to maintain pH balance
Conserve nutrients: glucose and protein
Eliminate toxins and end products of nitrogen metabolism: urea and creatinine
Other roles: blood pressure regulation, regulation of acid secretion in the stomach, regulation of body temperature and platelet aggregation, activation of vitamin D and controlling inflammation
What does the kidney produce
Renin: an enzyme that aids in controlling blood pressure
Erythropoietin
Prostaglandins: fatty acids that stimulate smooth muscle contraction
What is the physiology of the renal system
Blood enters the kidney via the renal arteries into the glomerulus of the nephron
Almost all water and small particles pass into the collecting tubules
Each nephron has parts that reabsorb or secrete certain solutes; the amount of solute that the kidney is able to reabsorb is pre-decided → renal threshold
Approximately 99% of water is reabsorbed by the kidney, remaining water (excess) is excreted as urine
Tests to evaluate kidney function are performed on urine and blood
What does azotemia mean
Azotemia refers to an increase in BUN and creatinine
Rarely only one of the two is elevated
What does uremia mean and why might this happen
Uremia refers to an increase in BUN and creatinine that is severe enough to cause the animal to feel ill
Animals will be dehydrated, inappetence and lethargic
They may also be vomiting and have diarrhea, have “uremic” oral and/or gastric ulcers and central nervous dysfunction
This is seen with advanced renal disease
Where does prerenal azotemia occur
Pre-renal azotemia–the underlying cause of the azotemia is occurring “before” the kidney
Where does renal azotemia occur
Renal azotemia – the underlying cause of the azotemia is occurring within the kidney
Where does post renal azotemia occur
Post-renal azotemia – the underlying cause of the azotemia is occurring “after” the kidney
What causes prerenal azotemia and what does it look like
Dehydration is the most common underlying cause
PCV and TP may be mildly elevated
Urine specific gravity (USG) will be elevated -the urine is well concentrated because the animal’s kidneys are functioning normally and are conserving water
What causes renal azotemia
Can be due to renal failure, congenital disorders, or pyelonephritis
Renal failure can be classified as acute or chronic
Acute–often very severe, sudden onset, often (but not always) younger animals; may be associated with known toxin exposure
Chronic–gradual decrease in renal function and onset of clinical signs
What does a cehm panel with renal azotemia look like
PCV and TP may be elevated if the animal is dehydrated (they often are, especially as the disease progresses)
The animal may become anemic with end stage, chronic renal disease due to decreased production of erythropoietin
USG will be decreased (the urine will be dilute)
What causes post renal azotemia and what does it look like
An obstruction in the ureter, neck of the bladder or urethra can cause a post renal azotemia
These animals are often dehydrated so PCV and TP will likely be elevated
USG will be elevated (the urine is well concentrated)
What is BUN and what does it do
BUN is the principal end product of aa breakdown in mammals
Used to evaluate kidney function due to the kidneys ability to filter urea from the blood
Increased BUN does not guarantee an absolute diagnosis of kidney disease
How does the BUN normally work within the renal system
All urea passes through the glomerulus into renal tubules
About half of the urea is reabsorbed into the bloodstream and the other half is excreted in the urine
What does BUN do when something is wrong in the renal system
Urea is not transported into the renal tubules as efficiently
When the blood exits the kidney back into circulation, there is an increased concentration of urea
Non renal causes of an increased BUN include and why
Dehydration- urea is insoluble, high volumes of water are needed for its excretion in urine
High protein diets or strenuous exercise – leads to an increase in protein breakdown
BUN can be evaluated with automated analyzers OR with semi quantitative dipstick – you will perform both of these in the lab
Where is serum creatinine formed
Creatinine is formed from creatine (a component of muscle) as part of muscle metabolism
During muscle metabolism, creatinine diffuses out of the muscle cells into body fluids and blood
Creatinine levels are influenced by the animals muscle mass
When is serum creatinine altered
Normally blood creatinine is actively filtered out of the blood and into the renal tubules
Any condition that alters the glomerular filtration rate (GFR) will alter the creatinine concentration in the plasma
Renal function has to be reduced by almost 75% before blood creatinine levels increase
Creatinine alone is not an accurate indicator of renal function
Blood BUN/Creatinine ratio is and affected when
Urea and creatinine are limited in their use for evaluating renal disease because their reference ranges are too wide
GFR can be as much as 4 times below normal before changes in urea and creatinine are observed on bloodwork
They will both be increased in renal disease
Both urea and creatinine are filtered by the glomerulus but the tubular reabsorption of urea can be regulated whereas creatinine stays constant
The use of this ratio is not well established in veterinary patients
Symmetric Dimethylarginine (SDMA) is a test used for and when
This is a test that is unique to idexx at this time
It can be run at one of the idexx referral labs or on their house analyzers
SDMA is a more sensitive indicator of kidney function – it will be increased with as little as 25% loss of renal function
It is usually elevated before creatinine and BUN are increased
It is a more reliable indicator of a kidney function than creatinine because it is kidney specific
What does SDMA tell you
Increased levels may be an indicator that another disease process is affecting the kidneys
IRIS guidelines now include SDMA measurements in their criteria for categorising kidney disease
What does the SDMA test detect
Diseases of the kidney at an earlier stage
CKD
Acute kidney injury
Pyelonephritis
Upper urinary obstruction
Kidney stones
Glomerulonephritis
Congenital disease
What does SDMA reflect
Other disease processes affecting the kidney
Hyperthyroidism
Vector borne disease
Systemic hypertension
Cardiorenal syndrome
Lower urinary obstruction
Sepsis
Neoplasia
Drug toxicity
Cystatin B test is and used when
NEW TEST available through idexx for canine and feline patients
Crystatin B is a protein that is found within the renal tubular cells
When renal tubular cell injury occurs, cystatin B is released into the urine
What does increase in Cystine B indicate
Increased levels of cystatin B in the urine indicate active kidney injury
Able to detect changes earlier than with bloodwork alone
Increased ability to recognize subclinical changes
Not used to analyze kidney function
SDMA, creatinine, BUN and USG are measured to evaluate renal function
Urine protein/creatinine ratio (UPC) is tested how
Proteinuria may be an indicator of glomerular dysfunction
Reference ranges available for canine and feline patients
2mL of urine is collected, ideally by cystocentesis
This test can be run by some in house analyzers or sent to a referral lab
What are the normal and abnormal UPC
UPC ratio <0.2 = Normal
UPC ratio 0.2-0.4 (0.2-0.5)= Borderline proteinuric
UPC ratio >0.4 (cats), >0.5 (dogs) = Proteinuric
Uric acid is produced where
Uric acid is a by-product of nitrogen breakdown
In mammals, it is normally converted to allantoin and excreted in the urine
Dalmatians–impaired ability to convert uric acid to allantoin so they excrete uric acid in the urine
In birds, uric acid makes up 68-80% of the total nitrogen that they excrete in urine
With renal disease, serum concentrations of uric acid will increase with >70% loss of renal function
What tests evaluate glomerular function
May be performed in patients with azotemia or in those that are showing clinical signs of renal disease in the absence of azotemia
There are two primary types of renal clearance tests
Effective renal plasma flow (ERPF)–utilizes substances that are eliminated by both glomerular filtration and renal secretion
GFR– only uses substances that are eliminated by glomerular filtration
Urine and blood are taken at specific times following administration of the test substance
Several different tests can be used to evaluate glomerular function such as
Creatinine clearance tests– endogenous and exogenous clearance tests, iohexol clearance test
Single-injection inulin clearance test
Water-Deprivation Tests
Vasopressin Response Test
Fractional Clearance of Electrolytes
Inorganic Phosphorus
Enzymuria
Endogenous and Exogenous creatinine clearance tests does what
Require measurement of blood and urine creatinine levels
The urinary bladder is catheterized and rinsed out at the beginning and at the end of the test
All voided urine is collected for 24 hours
Iohexol Clearance Test is performed how
Iohexol is given IV after a 12 hour fast
Serum samples are taken 2, 3 and 4 hours after administration and sent to a referral lab for evaluation
What is the purpose of the water deprivation tests
The purpose of a water deprivation test is to identify whether or not the kidneys are able to concentrate urine
Normally anti-diuretic hormone (ADH aka vasopressin) from the brain signals the kidneys to retain water
These tests involve dehydrating the patient to the point where the patient should be secreting ADH to promote water retention, and therefore increasing urine concentration
If urine concentration does not increase, this can indicate a lack of ADH, or nephrons that are unresponsive to ADH
How does a water deprivation test work
PU/PD can be seen with renal disease along with several other disease states
Diabetes mellitus and insipidus, Cushing’s disease, psychogenic polydipsia
Therefore, the kidneys may be functioning normally, they may not be getting the signal to concentrate urine OR polyuria may be the physiological consequence of polydipsia (as with psychogenic polydipsia)
Basic water deprivation test vs. modified water deprivation test
Inulin clearance test is and used for
Inulin is excreted entirely by glomerular filtration, therefore it may be the best test for evaluating GFR
Inulin is injected IV after a 12 hour fast
Serum samples obtained at 20, 40, 80 and 120 minutes after injection to measure inulin concentration
How to you perform a vasopressin response test
Performed when the patient is not able to concentrate their urine during the water deprivation test
Exogenous ADH is given, USG and urine osmolality are evaluated
Fractional Clearance of Electrolytes is done when
This is a calculation that describes the excretion of electrolytes (usually sodium, occasionally potassium and phosphorus) relative to the GFR
Differentiates pre-renal from post-renal azotemia
Inorganic Phosphorus (Pi) id done how
Serum Pi is usually the reciprocal of serum Ca
Initially, renal damage that alters the GFR leads to decreased urinary Pi and increased urinary Ca
Serum Ca and Pi levels are also affected
Enzymuria is and how to test for it
Refers to the presence of enzymes in the urine
Enzymes that may be present in the urine of patients with renal disease include: GGT and NAG which are released from damaged renal tubular cells
A comparison of enzyme levels to creatinine can give an indication of the extent of renal damage
Renal enzyme levels will increase rapidly after nephrotoxicity occurs
What does the pancreas do
Within the exocrine tissue are small “islands” of cells called islet of Langerhans
These make up the endocrine tissue
What cells are present in the islets of Lnagerhans and what percent
Alpha cells: almost 20% of the cells in the islets, secrete glucagon and somatostatin
Beta cells; ~80% of the cells in the islets, secrete insulin
Delta cells: <1% of the cells in the islets, secrete somatostatin
Pancreatic polypeptide (PP) cells: <1% of the cells in the islets, secrete pancreatic polypeptide
The pancreas has a limited ability to regenerate; when islets are damaged the tissue becomes firm and nodular
Exocrine pancreas tests test for what
Exocrine gland - a gland that secrete products through ducts rather than directly into the bloodstream
Amylase and lipase are common enzyme tests to evaluate for pancreatitis
Both can be within the normal range in cats with pancreatitis
Amylase is and does what
The primary source is the pancreas, but also found in salivary glands and SI
Breaks down scratches and glycogen
When is amylase increased
Blood amylase levels increase in
Acute and chronic pancreatitis
Obstruction of the pancreatic ducts
Intestinal obstruction/perforation
If there is a decrease in GFR, there may be an increase in amylase
Amylase that is greater than 3 times the normal range is suggestive of pancreatitis
The rise in concentration is not directly proportional to severity of disease
What is lipase and what does it do
Derived mostly from the pancreas
It breaks down the long chain fatty acids of lipids
Levels tend to be normal during early stages of pancreatic disease and gradually increase over time
In chronic pancreatic disease, damaged pancreatic cells are replaced with connective tissue that is unable to produce enzymes → both amylase and lipase begin to decrease
Canine and feline lipase can be tested using ELISA immunologic methods
Serum cPL and fPL SNAP tests
Trypsin in the pancreas is and does what
Trypsin is a proteolytic enzyme that catalyses the reaction that breaks down proteins
Produced exclusively in the pancreas
Produced exclusively in the pancreas
Where do you nromaly find trypsin
Trypsin is readily detected in feces, many tests are performed on fecal samples
The absence of trypsin in a fecal sample is abnormal
Not commonly used
When do you use serum trypsin
Serum trypsin-like immunoreactivity (TLI) is an immunoassay test that uses antibodies specific to trypsin and trypsinogen (the precursor to trypsin) to measure levels in the blood
Used to diagnose exocrine pancreatic insufficiency (EPI)– levels will be below the normal range in affected animals
May be performed with folate and cobalamin (B12) tests as well
This test is only available for dogs and cats
Overnight fast is required
Endocrine pancreas test test what
Endocrine Gland–glands that secrete hormones directly into the circulatory system
Blood glucose,fructosamine,β-hydroxybutyrate,serum cholesterol and triglycerides as well as urinalysis provide information about pancreatic function
Glucose is and increases when
Pancreatic islets respond directly to blood glucose concentration→they release insulin from the beta cells or glucagon from the alpha cells to regulate blood sugar levels
Because only insulin lowers blood glucose levels, if insulin is under-produced or under- performing, it will be clinically obvious
Blood glucose levels are the net balance between glucose production (food intake, conversion from other carbohydrates), glucose use and storage
Glucose uptake and metabolism depends on insulin and glucagon secretion from the pancreas
What happens if glucose tests are abnormal
If insulin levels are ↑, the rate of glucose absorption into cells for metabolism will ↑ → this will cause blood glucose levels to go ↓
If insulin levels are ↓ (as with diabetes mellitus), glucose is not absorbed into cells→this cause blood glucose levels to go ↑
Glucose tolerance test works how
This test challenges the pancreas and evaluates the effects of insulin
A glucose bolus is given and then blood and urine glucose concentrations are monitored
If there is adequate insulin production and the cells are responding appropriately, blood glucose levels should peak about 30 mins after glucose administration and return to normal within 2 hours
Glucose should not appear in the urine
What does a glucose tolerance test diagnose
Diabetes mellitus–prolonged hyperglycemia, glucosuria
Hyperactive Beta-cell Tumors– profound hypoglycemia
Other concurrent endocrinopathies can affect results
This test is rarely necessary to diagnose diabetes mellitus; persistent high blood glucose levels, glucosuria, a history of PU/PD, weight loss, +/- polyphagia are sufficient for diagnosis
This test may be used for animals that are borderline hyperglycemic or to differentiate stress hyperglycemia from diabetes mellitus
What is Fructosamine and how do you test it
Fructosamine is formed when glucose in the bloodstream binds to proteins
If there is a persistent hyperglycemia,fructosamine levels will be elevated
This can be run on some in clinic analyzers or may be a referred out test, fasting is not required
This test will give us an indication as to what the blood sugar levels have been doing for the past 2-3 weeks
It may be used for long term monitoring of diabetic cats, it can also be used in the diagnosis of suspect cases of diabetes mellitus
What does the insulin tolerance test and how does it work
A fasted blood glucose sample is obtained, then the patient is injected with a short-acting insulin
Subsequent blood glucose measurements are taken at 30 minute intervals for 3 hours
If serum glucose fails to drop to 50% of the fasting level within 30 minutes, then it can be concluded that insulin receptors are unresponsive or the insulin is being antagonized
Insulin resistance profoundly affects the animal’s therapy and prognosis
The patient needs to be monitored closely for signs of hypoglycemia during the test
Need to have glucose solution on hand to administer if necessary
Insulin / glucose ratio is tested when and what does it mean
Simultaneous measurement of fasting serum glucose and insulin can identify the cause of hyperinsulinemia
Hypoglycemia normally inhibits insulin secretion,however, pancreatic beta cell tumors (insulinomas) are hyperactive and unresponsive to glucose and secrete an abundance of insulin
Animals with hyperinsulinemia may have a “normal” fasting insulin, but the RATIO is often abnormal
Functions of electrolytes
Maintenance of water balance
Maintenance of fluid osmotic pressure
Muscular and nervous functions
Maintenance and activation of several enzyme systems
Acid-base regulation
What are electrolytes
The positive and negative ions found in all body fluids of all organisms
What are the negative ions of the elctrolytes
Anions - Chloride (Cl-), Bicarbonate (HCO3-) and Phosphate (PO4-)
What are the cations of electrolytes
Cations–positive ions
Sodium (Na+), Potassium (K+), Calcium (Ca2+),Magnesium (Mg2+), Hydrogen (H+
What does the acid base balance refer to
Acid-base balance refers to the steady state of the pH in the body
pH describes the hydrogen ion concentration in the body
Every change on the pH scale of one number represents a power of ten difference in H+ concentration
Normal pH is 7.35-7.45
What does the change in blood pH indicate
Acidosis–pH <7.3 → There is an excess of H+ ions in the peripheral blood
Alkalosis– pH >7.45→ There is a deficiency of H+ ions in the peripheral blood
What is a buffer system for in an acid base balance
In general, normal metabolic processes result in the production of acids (lactic acid, ketoacids, etc)
Buffer systems work to counter the buildup of acids by altering the concentration of hydrogen ions
What systems work to regulate pH
Respiratory→responds in minutes
Renal/Metabolic→responds over days
Bicarbonate buffer is and works for
If the blood pH becomes too acidic, bicarbonate binds to excess hydrogen ions → carbonic acid→ breaks down to water and carbon dioxide which is removed by respiration
HCO3-+H+ ←>H2CO3 ←>H2O + CO2
The kidneys regulate bicarbonate by reabsorbing or secreting it into the glomerular filtrate in response to the blood pH
Potassium buffer is and works how
K+ and H+ are both positively charged ions that move freely between intracellular fluid (ICF) and extracellular fluid (ECF)
A decrease in plasma K+ results in K+ moving out of the cells and into the ECF, H+ moves into the cell → blood pH becomes more alkaline
An increase in plasma K+ causes the opposite to occur: extracellular K+ moves into the cell and H+ moves out→ blood pH becomes more acidic
Protein buffer is and works how
Proteins bind and release H+ions
Hemoglobin has the ability to bind CO2 and H+
CO2 is transported to the lungs and exhaled
Acidosis and alkalosis are how
by the cause of the condition
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis
Is the pH of blood caused by one or more factors
The imbalances are inter-related
If a pH imbalance occurs, the respiratory and renal systems will work to correct the abnormality
Any condition that results in an accumulation of acids in the body leads to a metabolic acidosis
Ketoacid production due to DM→Decreased HCO3- → Metabolic Acidosis
Abnormal electrolyte concentrations and loss of acid d/t vomiting → Increased relative HCO3- → Metabolic Alkalosis
Electrolytes are affected by:
Increased or decreased dietary intake
Shift of ions between intra- and extracellular fluid
Renal loss or retention
Gastrointestinal malabsorption
Respiratory system
*Lipemia and hemolysis can affect electrolyte measurements
*Arterial samples are ideal for analysis of blood gases; must be analyzed quickly after collection because room air affects the concentration of dissolved gases and sample pH
The major electrolytes that we measure are:
Sodium
Potassium
Calcium
Magnesium
Hydrogen
Chloride
Bicarbonate
Inorganic Phosphorus
What will hemolysis affect and why
Chemistry panels measure the ions and compounds present in the serum/plasma ONLY, it does not measure the concentration of these products within the cells
With EXTRACELLULAR ions → hemolysis will dilute the sample causing ion levels to be artificially low
With INTRACELLULAR ions → hemolysis will cause ions to be released into the extracellular fluid thereby artificially increasing ion levels
Why and how do we measure sodium
The major cation of plasma and ECF
It’s main function is water distribution and maintenance of body fluid osmotic pressure
Sodium is filtered by the kidney and reabsorbed back into the body as needed in exchange for H+
Vital role in the pH regulation of urine and acid-base balance
Hypernatremia means
increased blood sodium concentration
Seen with water deprivation, hyperventilation, osmotic diuresis
Hyponatremia means
decreased blood sodium concentration
v/d, ketonuria, hypoadrenocorticism, CHF
What is potassium important for
The major intracellular cation
Important for muscle function, respiration, cardiac function, nerve impulse transmission and carbohydrate metabolism
Hyperkalemia means
increased blood potassium concentration
This may be seen with cellular damage, acidosis (K+ is exchanged for H+ to buffer pH), urinary tract obstructions
Hypokalemia means
decreased blood potassium concentration
Due to low intake, alkalosis, fluid loss d/t v/d, ketonuria, diuresis
What happens when potassium levels change and what samples fo you use to test it
Both extremely high and extremely low potassium levels can cause fatal cardiac arrest due to an abnormal heart rate
Plasma samples are preferred over serum samples as platelets can release K+ during the clotting process– however analyzer type may dictate sample requirements
If the sample is going to be refrigerated, the plasma should be separated from the cells – refrigeration will cause K+ to move from the ICF to the ECF
Chloride is what and how to test
Chloride is the predominant extracellular anion
It maintains water distribution, osmotic pressure, normal anion/cation ratio
Closely related to sodium and bicarbonate levels
Hyperchloremia– increased blood chloride concentration
Hypochloremia– decreased blood chloride concentration
If the sample is to be stored, serum/plasma should be separated from the cells to prevent artificial reductions in Cl- concentrations
Bicarbonate is and used for
The second most common anion in plasma
The kidneys work to regulate bicarbonate levels by excreting excesses after it reabsorbs what is needed from the urine
Bicarbonate levels are commonly estimated (not directly measured) from blood CO2 levels– this is done by a blood gas analyzer or as part of an electrolyte panel on a chemistry analyzer
Magnesium is and used for
2nd most common intracellular cation
Found in all body tissues, more than 50% is found in bones
Works closely with calcium and phosphorus
Activates enzyme systems, involved in making and breaking down acetylcholine (a neurotransmitter)
Imbalance of magnesium/calcium ratio can result in muscle tetany because of the release of ACh
Cattle and sheep are the only domestic animals to show clinical effects of magnesium deficiencies
What are changes in magnesium called
Hypermagnesemia– increased blood magnesium concentrations
Hypomagnesemia – decreased blood magnesium concentrations
Calcium is where in the body
More than 99% of calcium is found in bone
The remaining 1% helps to maintain enzyme activity, plays a role in blood coagulation, neuromuscular excitability and tone (decreased calcium can also result in muscle tetany), and maintenance of inorganic ion transfer across cell membranes
Calcium is inversely related to phosphorus, if one goes up, the other goes down
What is an imbalance in calcium called
Hypercalcemia– increased blood calcium concentration
Hypocalcemia – decreased blood calcium concentration
Very tightly regulated
What is phosphorus and how is it measured
80% of phosphorus is found in bones
The remaining 20% serves to store, release and transfer energy, is involved with carbohydrate metabolism and is used to produce nucleic acids and phospholipids
Within serum/plasma, phosphorus is in an inorganic form
Within RBCs, it is in an organic form
DO NOT USE HEMOLYZED SAMPLES – falsely elevated results
Separate the cells from the serum/plasma ASAP
What is an imbalance in phosphorus called
Hyperphosphatemia– increased serum phosphorus levels
Hypophosphatemia – decreased serum phosphorus levels
Anion gap is
Normally, the total number of cations EQUALS the total number of anions
This neutrality is maintained by the various buffering systems
Any difference between positive and negative charges is called the anion gap
Chiefly used to identify metabolic acidosis
How do you calculate the anion gap
(Na+ + K+) –(Cl-+HCO3-) = ANION GAP
What is a normal anion gap and what causes an imbalance
Dogs: 12-24mEq/L
Cats: 13-27mEq/L
Increased anion gap: lactic acidosis, renal failure, diabetic ketoacidosis
Decreased anion gap: often due to hypoalbuminemia →the proteins required to transport bicarbonate are lacking
Creatinine kinase (CK) is and found where
CK is an enzyme found predominately in striated muscle cells and to a lesser extent, the brain
When skeletal muscle (namely cardiac) is damaged, CK leaks out of the cells and results in elevated CK in the peripheral blood
CK is frequently tested if an animal has an elevated AST but shows not symptoms of liver damage
If the CK is also elevated, it would suggest a muscular issue (possibly cardiac related)
It is also elevated in CSF with non-specific damage to neural tissue (hypoxia, trauma, inflammation, space-occupying tumors)
CSF CK can also be useful prognostically in canine neurological cases and premature foals
What conditions cause an increase in CK
Seizures
Intramuscular injections, repeated attempts at IV blood draws
Surgery
Vigorous exercise
Electric shock
Lacerations
Bruising
Hypothermia
Persistent recumbency
Myositis and myopathies
Essentially anything that damages the cell membranes…
A delay in testing may cause an increase in reported CK levels
Lactate is
Lactate, or lactic acid, is produced by anaerobic cellular metabolism
Increased lactate indicates hypoxia or hypoperfusion
Lactate can be analyzed in plasma, CSF and peritoneal fluid
When and how to collect lactate
Blood/peritoneal fluid analysis is a diagnostic aid in equine colic cases
In healthy horses, the blood lactate is always higher than in the peritoneal fluid
If horses have a GI disorder such as an impaction or torsion, the peritoneal fluid lactate will be higher than the blood lactate levels
Collect sample in fluoride oxalate or lithium heparin tubes
Hand held lactate meters are available
Endocrine system assays are
There are a variety of endocrine organs and tissues that produce and release hormones directly into capillaries
These include the adrenal glands, thyroid and parathyroid glands and the pituitary gland
Adrenocortical function tests is
Stressors cause the hypothalamus to secrete corticotropin - releasing hormone (CRH) → causes the anterior pituitary to secrete adrenocorticotropic hormone (ACTH) → stimulates adrenocortical growth and secretion
Cortisol is an important hormone that is secreted by the adrenal gland in mammals
Cortisol inhibits both CRH and ACTH release
What is cushings and what causes it
Hyperadrenocorticism/Cushing’s Disease
Excessive cortisol release
It is caused by:
Brain/pituitary tumors
Idiopathic hyperplasia of the adrenal glands
Neoplasia of one or both adrenal glands
Over- enthusiastic use of glucocorticoids
What is addisons and what causes it
Hypoadrenocorticism/Addison’s Disease
Reduced cortisol release
May be caused by:
Adrenal atrophy
Autoimmune disease
Neoplasia
Medications
Adrenocorticotropic hormone stimulation test is and used for
An ACTH stimulation test may be requested for animals presenting with suspected hyper- or hypoadrenocorticism
This test evaluates the adrenal glands response to the administration of ACTH
The degree of glucocorticoid production is expected to be proportional to the adrenal gland’s size and development
Hyperplastic (cell proliferative)–exaggerated adrenal response
Hypoplastic (atrophied)– decreased adrenal response
This test can be used to detect abnormalities but not the underlying cause
Also used to evaluate the efficacy of therapy
ACTH test interpretation – cushing’s disease
Cortisol levels are tested before and after ACTH administration
Accuracy in diagnosing hyperadrenocorticism with this test is about 80% in dogs and 50% in cats
Used to evaluate response to mitotane or trilostane therapy
Clinical signs of Cushing’s Disease
PU/PD, panting, polyphagia, pot-bellied abdomen, altered fat distribution, alopecia, mild muscle weakness, lethargy
Fragile skin syndrome in cats
ACTH test interpretation – addison’s disease
Cortisol levels are tested before and after ACTH administration
The adrenal glands are unable to respond to the ACTH so post-ACTH cortisol levels are below the normal range
Clinical signs of Addison’s Disease
Depression, lethargy, lack of appetite, weight loss, v/d, bloody stools, weakness, dehydration and bradycardia
Dexamethasone Suppression Tests: is and how to perform
Low Dose Dexamethasone Suppression Test (LDDST)–can confirm a diagnosis of Cushing’s disease or can be used in the place of the ACTH stim test to diagnose Cushing’s disease
High Dose Dexamethasone Suppression Test (HDDST) – used to differentiate between pituitary causes of hyperadrenocorticism from adrenal causes
Dexamethasone is a potent glucocorticoid that suppresses ACTH release
Interpretation of the LDDST:
Adrenal dependent–no cortisol suppression at 4 or 8 hours post dexamethasone
Pituitary dependent–cortisol suppression at 4+/- 8 hours post dexamethasone
Interpretation of the HDDST or UHDDST:
Adrenal dependent – no cortisol suppression
Pituitary dependent– cortisol suppression
Combined dexamethasone suppression and ACTH stim tests is
Dexamethasone is administered IV, ACTH is then administered by the IV route 4 hours later
Cortisol levels are measured before dexamethasone administration, before ACTH administration and after ACTH administration
Combined dexamethasone suppression and ACTH stim tests how to interprate
Increased cortisol after dexamethasone and ACTH Stim – Hyperadrenocorticism
Increased cortisol after dexamethasone and NORMAL after ACTH stim – hyperadrenocorticism
Increased cortisol after dexamethasone and VERY HIGH after ACTH stim – pituitary hyperadrenocorticism
Adrenocortical function tests is done when
Urine Cortisol/Creatinine ratio – used as a screening tool to rule out Cushing’s disease
If the ratio is low – it is very unlikely that the animal has hyperadrenocorticism
If the ratio is elevated, further testing needs to be done to confirm a diagnosis of hyperadrenocorticism
Equine cushings idease is/signs/diagnosis
Tends to occur in older horses
Due to adenomas of the pars intermedia of the pituitary gland
Clinical signs include: PU/PD, polyphagia, muscle weakness, excessive sweating, long hair coat (fail to shed)
Lab findings include: hyperglycemia and glucosuria (likely due to insulin resistance)
Diagnosed with an overnight dexamethasone suppression test
Insulin and anti-adrenocortical medications are not useful, dopamine antagonists may be helpful
thyroid hormones infleunce what
Thyroid hormones influence the metabolic rate, growth and differentiation of cells
How do thyroid hormones work
Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the anterior pituitary to release thyroid stimulating hormone (TSH)
TSH enhances thyroid gland growth, function and release of thyroxine which is produced in two forms
T3 (triiodothyronine; the more active form)
T4 (thyroxine; can convert to T3 in tissues)
Thyroxine inhibits TRH and TSH release
Thyroid disease primarily manifests as:
Hypothyroidism: Dogs, horses, ruminants and swine
Hyperthyroidism: Cats
This may be attributable to dietary iodine imbalances or exposure to goitrogens in large animals
How do you dignose thyroid problems in food animals
Clinical signs–spontaneous abortion, stillbirths, alopecia, goiter in fetuses
Serum T4 concentrations
Protein bound iodine levels in serum
Pasture iodine analysis– the feed may be analyzed for goitrogenic plants or for excess calcium (which decreases iodine uptake)
A primary glandular disease due to neoplasia, autoimmune disease or idiopathic atrophy is much more common than pituitary disease
Some drugs/medications affect T4 concentration such as
Insulin and estrogen increase T4
Glucocorticoids, anticonvulsants, penicillin, trimethoprim sulfamethoxazole (TMS) and others decrease T4
How do you diagnose thyroid issues with companion animals
measuring free T4, +/- TSH levels
Hypothyroid: low free T4 and elevated TSH
Hyperthyroid: elevated free T4
Goitrogens is
Substances that disrupt the production of thyroid hormones, interfering with iodine uptake in the thyroid gland
Brassica spp
This triggers the release of TSH from the pituitary gland and promotes the growth of thyroid tissue → GOITER
Thyroid hormone test in horses
In horses, iodine- deficient hypothyroidism is rare since iodized salt is available
However, overzealous iodine supplementation can actually provoke hypothyroidism and goiter because the excessive use of iodine can actually inhibit thyroid function!!
Additional thyroid function tests are
T3 – less reliable than free T4
Total T4 (TT4) – will also measure anti-thyroid hormones so not as reliable as a free T4
Thyroglobulin autoantibody test – canine specific test, used to detect autoimmune thyroiditis
Thyroid stimulating hormone response test: primarily used for research purposes at this time
Pituitary function testing
Elevated growth hormone (GH), produced by the pituitary gland, will cause canine acromegaly
Serial assays of GH are tested because dogs with acromegaly will show a constant level of GH
In a normal dog, the GH levels will fluctuate
Gastrointestinal function tests are and done when
The principal function of the GIT is to digest and absorb nutrients and excrete waste products
GI diseases are common in animals, so specific testing and diagnosis is important
Biopsy is may be required to arrive at a definitive diagnosis; function tests rule out other diseases and confirm the need for more invasive procedures
Maldigestion → due to altered gastric secretion or reduced digestive enzymes (from the pancreas and to a lesser degree the small intestine)
Approximately 90% of the pancreas needs to be non-functional before clinical signs become apparent
Malabsorption→ often caused by disease of the small intestinal wall or bacterial overgrowth syndromes
A loss of function of >50% of the small intestine in dogs will result in “short bowel syndrome”
Fecal occult blood is and looks like
Blood loss into the gut may be apparent as either melena or hematochezia depending on where the bleeding is occurring within the GIT
If blood loss is less severe, it may not be apparent by gross examination of the feces
If blood loss into the GIT is suspected, a fecal occult blood test can be run
This test will produce a color change if it comes into contact with hemoglobin or myoglobin
Small animals will need to be fed a meat free diet for up to 3 days prior to testing
Ensure large animals are not being supplemented with meat or bone meal
d-Xylose Absorption Test is
d-Xylose is absorbed in the SI and eliminated unchanged in the urine
This makes it relatively easy to trace
Primarily performed in horses, can also be used in dogs
Not useful in ruminant species–rumen flora interfere with results
Xylose is given orally and serial blood concentrations are measured every 30 minutes for 4-5 hours
Abnormal test results suggest a malabsorptive problem in the SI
Vomiting and ascites will decrease xylose blood concentrations
Renal disease will lead to an increase xylose blood concentrations
Serum Folate and Cobalamin (B12) is
B vitamins that are reduced in animals with malabsorption issues
Folate is absorbed in the proximal intestine, while cobalamin is absorbed in the ileum
Bacterial overgrowth may cause folate levels to increase and cobalamin levels to decrease
Often evaluated in conjunction with TLI
Overnight fast required prior to blood sampling
Toxicology samples are done when and how
Samples for toxicology are usually sent out to a reference lab
Fluids, tissues and feed must be sent in separate, clean, leak-proof, hard, plastic containers
Samples must be individually identified with the owner’s and veterinarian’s names, animals name/ID number and specimen type
Samples can include serum/plasma, urine, feces, feed, water, suspicious bait, stomach contents (in the form of vomit, gastric lavage or post mortem collection)…
Blood samples are best kept refrigerated, gut contents may be frozen
Samples may also include necropsy or biopsy tissues→ they should be placed in a 10% formalin solution in a 10:1 formalin to tissue ratio
May become a legal issue!!!
Lead poisoning is and caused by
Fairly common environmental pollutant–found in old paint, ammunition, car batteries, solder, linoleum, petroleum and roofing products
“Plumbism”, lead poisoning can occur in all species, clinical signs are related to the GIT and nervous systems
Hematology examination may exhibit basophilic stippling of RBCs and increased nucleated RBCs without anemia
There will not be any specific changes on the chemistry panel
Blood collected in EDTA, heparin or citrate may be analyzed for lead at a reference lab
Feces, liver, kidney, or bone can be analyzed for the presence of lead
nitrate/nitrite poisoning is and how to test
Most common in ruminants, pigs, and horses that ingest feeds containing high concentrations of these compounds
Excessive levels may be found in cereals, grasses and root crops that have been heavily fertilized with nitrogenous compounds
Water may contain large quantities of nitrate
Nitrates are converted to nitrites in the feed or the GIT; nitrites absorbed from the gut decrease the oxygen-carrying capacity of the RBCs by degrading hemoglobin to methemoglobin → the animal’s blood becomes dark red to brownish in color
A dilute diphenylamine solution may be used to test for nitrites in feed, serum/plasma, urine and body fluid samples → if nitrates or nitrites are present in the sample, it will turn blue immediately
Hemolysis may mask the color change
Anticoagulant rodenticides look like and cause
These are chemicals that are designed to kill rodents
They work by inhibiting the metabolism of vitamin K
Vitamin K is needed for the production of clotting factors (II, VII, IX and X) in the liver
Affected animals will have a prolonged prothrombin and partial thromboplastin time as blood clotting is impaired
A presumptive diagnosis is made based on routine coagulation testing and patient response to vitamin K therapy
Chemicals that denature hemoglobin are
Ingestion results in oxidative damage to RBCs → Heinz bodies are formed
Horses–Red Maple leaves
Cattle–Brassicaspp
Dogs–Onions
Cats–Acetaminophen
Selenium deficient animals are more prone to oxidative injury
Ethylene glycol poisoning is and causes
Commonly causes accidental poisoning that can lead to a fatal toxicosis in dogs and cats
A diagnosis can be presumed based on urinalysis and the observation of a high concentration of calcium oxalate monohydrate crystals
5mL (one teaspoon) can kill a cat, 15mL (one tablespoon) can kill a medium-sized dog
The formation of urinary crystals causes irreversible kidney damage
Ethylene glycol → Glycolic acid → Oxalic acid crystals
Drug abuse and the chem panel
Clinical signs vary significantly depending on the drug that was ingested
Drugs can be medicinal or illicit
Keep in mind that owners may not want to disclose if their animal may have accidently ingested illicit drugs
It is always the room mate’s fault!!
Rapid screening tests are available for drugs of abuse, typically include THC, opioids, cocaine, meth
Also, illicit drugs may contain other drugs or stimulants as they are unregulated
