Investigation of Disease Lectures 1-3 Flashcards
What 2 fluids are usually tested in a clinical biochemistry lab?
Urine and Blood
What are the 3 main types of lab tests and what are their roles?
1) Diagnostic
- Investigating a symptomatic individual
2) Screening
- Identifying asymptomatic at risk individuals in a population
3) Monitoring
- checking health before procedure
- assessing individual after treatment
- monitoring long term or chronic condition
What is a Phlebotomist
Someone trained to take blood samples
What is venipuncture?
The taking of blood with a hypodermic needle from a vein
How are different blood samples identified and give an example
Different coloured caps used
Red - Plain serum
Yellow - Serum separator
What is the difference between serum and plasma?
Liquid part of normal blood is plasma
Liquid part after clotting is serum (lacks clotting proteins)
Name some pre analytic factors
Sample container Sample suitability - haemolysed - lipaemic - jaundiced Age of sample Medication IV fluids Venous statis
What are the 4 main benefits of lab automation?
More efficient
Improved health and safety
Error reduction
Improved patient care
What are the 4 main types of lab tests?
Colorimetric Enzymatic Electrochemical - pH, ions, biosensors Immunological - tumor markers etc
Explain the terms accurate and precise
When data points are close together = precise
When their mean value is close to actual value = accurate
What are reference ranges?
Used to define normality in order to identify abnormal results which may indicate disease
Name one problem with reference ranges
- Age and sex
(different at different ages and sex) - Biological variation
Serum creatinine may be outside of reference range for an old lady and a very muscular man although they may be healthy
What is quality control in the lab?
QC samples run on regular basis (daily) to maintain reliability
What are the 4 main functions of the kidney?
Filtration
Reabsorption
Secretion
Excretion
What would you expect as a sure sign in the blood of kidney failure?
Accumulation of urea levels (uraemia)
What is the BUN test?
Blood urea nitrogen test - common blood test to assess the amount of urea in blood
What 2 structures are contained in the renal corpuscle?
The glomerulus and the Bowmans capsule
What does the juxtaglomerular apparatus (JGA) consist of?
Afferent and Efferent arterioles
Macula densa
- part of the distal tubule
- cell mass that secretes renin
What range of molecular weight molecules are filtered and not filtered at the glomerulus? Give examples of such molecules
Molecules of
Why is glomerular filtration rate measured?
Decline is GFR is an indicator of kidney disease
How is GFR calculated?
(urine concentration of substance X urine ‘flow’) divided by plasma concentration of substance
What 3 criteria must the chosen substance meet?
- be freely filtered from plasma at glomerulus
- not be absorbed anywhere along the nephron
- not be secreted
What molecule was used in the past for GFR and how was it administered?
Inulin
Administered intravenously
What substance is now used in GFR?
Creatinine
What is the main method used to test for creatinine and how does it work?
Jaffe method
- Creatinine is reacted with alkaline sodium picrate to form an oramge-red complex
What are the 3 main problems with the Jaffe method and how can they be avoided
1) Non specificity
- other compounds can cause reaction eg proteins, glucose
2) Spectral interferences
from bilirubin, haemoglobin etc
3) Non standardized calibration
Can be addressed with good quality assurance
What is Creatinine and how is it formed?
Cyclic, internal anhydride of creatine
Formed when creatine cyclizes and loses a water molecule
Where and how is creatine made?
Made from L-arg, gly and L-met in kidney and then liver
Transported to muscles via blood
How and where is phosphocreatine used?
Used in tissue with high energy demands eg muscle and brain
Can be dephosphorylated to phosphorylate an ADP to ATP
What is the name of the study that estimates GFR using serum creatinine corrected by gender, body size, ethnic origin and age?
Modification of Diet in Renal Disease (MDRD) study
What other molecule can be used in GFR instead of creatinine?
Cystatin C
Why is cystatin C not commonly used?
Higher reagent costs than creatinine
In urinalysis, what do dipsticks measure?
Leucocytes (UTI) Nitrite (bacterial infections - convert nitrate to nitrite) Urobilinogen (Liver damage) Protein pH Hb (blood in urine - damage) Keto compounds Bilirubin (liver damage, jaundice, blockage to bile secretion) Glucose (diabetes)
What is microalbuminuria?
Pathological increase in the rate of loss of albumin in the urine
Why is it important to monitor albumin in the urine in patients with diabetes mellitus?
microalbuminuria is an early sign of diabetic nephropathy
How is microalbuminuria defined?
Amount of albumin in the urine below the limit of detection by conventional dipsticks
How should microalbuminuria be tested?
A sensitive method with an early morning urine (EMU) sample
What values in both men and women indicate microalbuminuria?
An albumin:creatinine ratio of 2.5mg/mmol or above for males or 3.5mg/mmol or above for females
What are the 2 types of kidney disease?
Acute and chronic
What is acute kidney injury?
Can cause metabolic derangment
Often high mortality
Commonly reversible
Give some examples of conditions that may result in chronic kidney disease
Diabetes mellitus
Hypertention
Glomerulonephritis
Polycystic kidney disease
CKD is classified into 5 stages based on what?
GFR
What are the values associated with the 5 stages of CKD?
Greater than 90 mL/min/1.73m2 (stage 1) 60-89 (stage 2) 30-59 (stage 3) 15-29 (stage 4) below 15 (stage 5 or established renal failure ERF)
What is ESRD?
End stage renal disease - when renal function is not enough to support life
What is diabetic nephropathy and how is it diagnosed?
CKD - Chronic hyperglycemia in the blood causing damage to the glomerulus capillaries
Diagnosed by increased protein in urine (proteinuria) and low but abnormally increased albumin excretion
How are hypertention and CKD linked?
Hypertension in addition to CKD accelerates ESRD
CKD can cause hypertensio due to fluid and salt retention and activaion of the sympathetic and renin-angtiotensin systems
Hypertention treated with ACE inhibitors or angiotensin receptor blockers (ARBs)
What is nephritis and what is interstitial nephritis? What are the 2 types of interstitial nephritis?
Nephritis is inflammation of the kidney (can be different areas)
Interstitial nephritis - most common, inflammation of interstitial tissue surrounding tubules
Acute (AIN) or Chronic (CIN)
What is renal tubular acidosis?
Group of kidney disorders due to defects in proximal tubule bicarbonate reabsorption or distal tubule H+ secretion, or both
What is polycystic kidney disease and what are the 2 types?
Inherited condition that causes cysts to grow in the kidneys.
Symptoms include hypertention and haematuria (blood in urine)
Autosomal dominant (ADPKD): 1 in 400 - 1 in 1000
Autosomal recessive (ARPKD): 1 in 10,000 to 1 in 40,000
What are the 2 most common electrolytes in biological fluids?
sodium and potassium
What is the approximate total water volume in an adult human?
42L
How much water is lost on average a day?
2L
What is the water distribution between the 2 main compartment (intracellular and extracellular)
ICF - 28L
ECF:
- plasma (3.5L)
- intertitial fluid (10.5L)
What is the main cation in extracellular and intracellular fluid?
Extracellular - Sodium
Intracellular - Potassium
How is partitioning maintained?
Using the Na/K pump
How does the Na/K pump work?
3 sodium moved out, 2 K moved in, using 1 ATP and 1 water molecule
3Na(in) +2K(out) + ATP + H20 —> 3Na(out) + 2K(in) + ADP + Pi
What is the response to water deprivation?
-Rising plasma osmolarity
- Detected by osmoreceptors causing:
1) Thirst
- increased liquid consumption
-increased body volume
2) ADH release from posterior pituitary
- Water retention
- Reduced urinary output
corrected osmolarity
How does the renin-angiotensin-aldosterone (RAA) system work?
- Low blood pressure and loss of blood volume stimulate juxtaglomerular apparatus of kidneys to produce renin
- Angiotensinogen, produced by liver, converted to angiotenin I by renin
- ACE converts angiotensin I to angiotensin II
- Angiotensin II causes range of physiological responses:
1) Acts on medulla, increasing sympathetic activity, increase heart rate
2) Tubular reabsorption of Na+, Cl- and H20, K+ excretion
3) Adrenal cortex of adrenal gland produces aldosterone (also causes 2))
4) Arteriolar vasoconstriction, increase blood pressure
5) Posterior pituitary gland produces ADH; H20 reabsorption
How does aldosterone work?
Causes production of new protein channels and pumps in lumenal side of distal tubule cells
How does ADH work?
1) ADH binds to blood side membrane receptors of collecting duct cells
2) Activates cAMP second messanger system
3) Cell inserts AQP2 water pores into luminal membrane
4) Water reabsorption into plasma
How does Atrial natriuretic peptide (ANP) work?
Released in response to arterial stretch (high blood volume)
- Does opposite to RAA system
- inhibits renin and aldosterone production
- reduces Na reabsorption
- acts an vasodilator
Name 3 reasons where assessing water and electrolyte balance may be required?
1) To identify is electrolyte abnormality is responsible for a patient’s clinical features
2) Detect abnormalities at time of hospital admission (v important in A&E)
3) monitor correction as response to treatment
Are electrolyte tests high or low error?
HIGH! One of the most open error tests
Care should be taken
How are electrolytes measured and what is measured?
Na and K routinely measured using ion selevtive electrodes (ISEs). Measures activity rather than concentration - closely related in dilute solutions
What are the 2 types of ISEs and what does each do?
Direct - read undiluted sample at electrode surface
Indirect - read samples diluted in buffer - used in automated analysers
What are multifunction ion selective field effect transistor (ISFET) detectors?
Ion detectors tha are capable of detecting H+, Na+, K+ and Ca2+
- will likely become increasingly common
What 2 specimens are accepted in labs for electrolyte testing and why cant other specimen tubes be used?
1) Serum
2) Lithium heparin plasma
Other specimen tubes have anticoagulants that contain salts of Na/K e.g EDTA
These are known as ‘artifacts’ and contaminate sample with Na or/and K
What are the 3 main criteria for arriving samples in order to minimise artifacts and why?
1) Not shaken
- shaking can lyse erythrocytes, releasing K
2) Cold storage
- inhibits Na/K ATPase
3) Rapid blood delivery
- Aged blood can release erythrocyte K
Why do Na levels of blood samples from inpatients need to be checked carefully for artifacts?
Most on saline drip
- contains approx 150mmol/L Na
What is the reference range for kalaemia (blood K)?
3.8 - 5.0 mmol/L
How is osmolarity defined
The concentration of a solution expressed as the total number of solute particles per litre
What is osmolality?
The number of osmotically active particles in solution, meausred in moles of solute/kilogram (Osm/kg)
What are osmotically active substances? Give examples
Any that interact with water (hydrogen bonding) to influence its partitioning across semi permeable barriers
Examples: ions, proteins, urea and glucose
What is a healthy osmolality?
Between 285 - 295 mOsm/kg in both extra and intracellular fluids (excluding the kidney)
What is used to measure osmolality?
Osmometer
What does a high and low osmolality mean?
High: there is less water than solute - water deficient
Low: more water than solute - water excess
What is he reference range of plasma sodium?
135 to 145 mmol/L
What are the 3 classifications of hyponataemias and what causes each?
1) Hypervolemic hyponatraemia
- loss of water and sodium increased but water loss is greater than sodium loss
- caused by congestive heart failure, liver failure, renal dysfunction
2) Euvolemic hyponatraemia
- body water increases as sodium is near normal
- caused by syndrome of inappropriate ADH (SIADH), water overload, hypothyroidism
3) Hypovolaemic hyponatraemia
- Deficit is water and sodium, but greater sodium loss
- caused by vomiting and diarrhoea, burns, diuretics
What is pseudohyponataemia?
A value of Na
What is SIADH and how is it treated?
Syndrome of inappropriate antidiuretic hormone ADH production continues even in low plasma osmolality (not enough salt) Hyponatraemia treatment (i.e saline drip) should try to reverse it SLOWLY (over days) or risk of permanent cerebral damage
What is hypernatraemia and how does it occur?
Elevated levels plasma sodium, usually due to water deficit
Causes:
Gastrointestinal losses e.g vomiting, cholera
Hot, dry conditions
Inadequate water intake
What are the 2 main a characteristics hypernatraemia in diabetes insipidus (DI)?
Characterised by production of a high volume of dilute urine (polyuria) and excessive drinking/thirst (secondary polydipsia)
How much urine does a DI patient produce a day on average?
6L (normal is 2L)
What are the 2 main types of DI?
Cranial and nephrogenic
What is cranial DI and how does it occur?
- Arises from failure to secrete ADH from the posterior pituitary
- Can be congenital, due to head injury or tumour)
What is nephrogenic DI?
Due to kidneys failing to respond to ADH
What test can be done to diagnose DI and what are the normal and positive results?
Water deprivation test
Normal - volume of urine will decrease and become more concentrated over time
Positive - High volume, dilute urine continues
What is the most apparent effect of potassium imbalances?
Effects on cardiac and skeletal muscle
How can both hypo and hyperkalaemia be detected?
Using an ECG
What is the effect of hypo and hyperkalaemia on muscles?
Hypo - muscle weakness, fatique and cardiac arrthythmias
Hyper - irregular heartbeat and even cardiac arrest
Describe the 3 main causes of hypokalaemia and treatment
1) Increased loss by kidneys (renal conditions or failure)
2) Increased loss by GI tract (diarrhoea, vomiting)
3) Redistribution from ECF to ICF
Treatmet:
- If deficient, high K food eg banana
- If more serious, intravenous
Describe some causes of hyperkalaemia and treatment
Due to increased release from cells to ECF or impaired secretion
- Acute or end stage renal failure
- Diabetic ketoacidosis
Treatment:
Over 7mmol/L - prompt action to prevent cardiac arrest (calcium or insulin can be given)
Mild hyperkalaemia - tackling causative factors
What is the distrubution of calcium in the plasma? (%)
- Free ionised (Ca2+) 47%
- protein bound (mainly albumin) 46%
- complexed (e.g citrate, phosphate) 7%
What is the most common cause of hypercalcaemia?
PTHrP (PTH related protein) is related in function to parathyroid hormone (PTH) which increases plasma calcium. PTHrP released by tumour cells
Where is calcitiol produced, what does it do and what does it cause if deficient?
- produced in kidneys
- vitamin D
- Stimulates re-absorption of calcium (kidney) or absorption (GIT) and deposition in bone
- Defects cause rickets in children and osteomalacia in adults
What is calcitonin?
- Antagonist of PTH
- Released by thyroid C cells in response to increased plasma calcium
- reduces calcium reabsorption (kidneys), absorption (GIT) and bone absorption
