C11 Laboratory Evaluation of the Liver & Exocrine Pancreas Flashcards
Normal Bilirubin Production & Metabolism
- Macrophages in the spleen phagocytose old RBCs, strip out iron and turn into into the storage form, hemosiderin
> Macrophages take heme from RBCs and make unconjugated bilirubin “Ubili”
> “Ubili” is attached to albumin, moves to the liver
> Ubili conjugated in the liver by hepatocytes, ie. they make it water soluble
> moves into intestine via bile duct as conj bili
Pre-hepatic Hyperbilirubinemia
- how does it arise? what builds up?
- if excess amounts of RBCs being ingested (eg. trauma?, IMHA, resolving giant clot, etc.), we have excess Ubili being formed, which all goes to the liver
> liver is overwhlemed
> unconjugated bilirubin is the form that predominates in this case
Posthepatic Hyperbilirubinemia
what do we see in blood?
how does this happen?
= Increased Cbili Regurgitated into Blood
- we can have things that block the bile ducts
* pancreatitis / cholangitis /
liver flukes / neoplasia / cholelithiasis
> anything that blocks the bile ducts will result in regurgitation of conjugated bilirubin into circulation
what bile-related phenomenon will we see in horses off feed for 12h
Horses off feed ~12 h
* Increased bilirubin
* Unconjugated > conjugated bilirubin
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- when horses are off feed, their liver cannot process bilirubin into conjugated bilirubin
Bilirubin – 3 Measurements on Biochemical Profile
- Total bilirubin – measurement of unconjugated & conjugated forms
- Unconjugated (or free) bilirubin – pre-hepatic hyperbilirubinemia
- Conjugated bilirubin – intra-hepatic or post-hepatic cholestasis
Lab Evaluation of Hepatocellular Injury / Function
- what can we look at on out regulat biochem? specialty tests?
Regular Biochem profile:
1. Liver enzymes
2. Liver products/clearance
Specialty tests:
3. Liver functiontests
liver leakage enzymes
Magnitude of Increase Does Not:
- Differentiate Cause or Severity of Injury
- Prognosticate
how will liver leakage enzymes appear in sublethal damage, necrosis, or cirrrhosis?
Sublethal Damage - Many cells with a little damage, large ALT increase
Necrosis - Few cells dying, can only release so much ALT (but this is serious damage)
Cirrhosis - Very few remaining cells, choked off from circulation by fibrosis; serum ALT may be normal due to lack of circulation or so few cells left
Hepatocellular Injury – Leakage Enzymes (U/L)
- Alanine aminotransferase – ALT
- Glutamate dehydrogenase – GLDH
- Aspartate aminotransferase – AST
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* Sorbitol (iditol) dehydrogenase – SDH
ALT is used for what species? what does it tell us and what is its timeline? not good for what animals?
- cat, dog
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Liver specific for hepatocyte injury or necrosis: - (Except severe muscle injury - must have corroborating evidence)
- ↑ ~12h after injury
- If damage resolves, returns to normal in 2-3 weeks
- Not useful in large animals or birds
ALT may increase with use of what drug class?
- May ↑ with anticonvulsants (causes damage)
investigate increased ALT further when? when is it very important to investigate?
*ALT 2x normal or persistently increased (~1 month)
> Even with marked increases in ALT, liver can regenerate within 3 d > nothing to see on biopsy
> Only biopsy if increased ~1 month
> Perform coagulation testing first!
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Very important to investigate:
*Middle-aged to older dogs – chronic hepatitis is common
*Cats with lymphoplasmacytic hepatitis
> Prompt diagnosis & therapy may increase survival time
*Young dog – consider portosystemic shunt
*Dogs with very poor oral health (+/- ↑ ALP)
AST is found in what species? what tissues is it found in? how do levels change over time?
- Cat, Dog, Horse, Bovine
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Not liver specific:
*Liver origin (compare to ALT)
*Muscle origin (compare to CK)
*RBCs (serum pink?)
*Pancreas (compare to lipase / amylase, etc.)
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Generally parallels ALT, not typically as high If damage stops, decreases over 2-3 weeks
GLDH is used for what species? what does it tell us?
Horse, Bovine, Birds
(also can be used for Cat, Dog)
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* Sensitive and specific for hepatocellular injury
* Uncommonly measured in USA – reagent availability
SDH is used as a liver marker for what species? limitations?
Horse, Bovine
(also can be used for Cat, Dog)
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* Stability & half-life are issues
> h if not refrigerated / frozen
* Used in USA for detection of liver damage
DDx Increased ALT AST GLDH
- Degenerative
> eg. CHF >. increased pressure on liver > damage - Infectious
- Inflammatory
- Metabolic
> Endocrinopathies eg. hypoadrenocorticism, hyperparathyroid in cats - Trauma
> Ischemia (blood loss/destruction & shock) - Neoplasia
> need a diffuse process eg. lymphoma - Toxins
> eg. acetaminophen, cyanobacteria - (Cholestasis)
> bile stuck next to lipid membranes > breaks them down - Hepatic lipidosis – NEB!
> Cats, ponies, donkeys, llamas, cows
> AST & ALP good for cats w. hepatic lipidosis
> GLDH horses, cattle, llamas
> Look at ketones
hepatic lipidosis enzymology for various species
Hepatic lipidosis – NEB!
* Cats, ponies, donkeys, llamas, cows
* AST & ALP good for cats w. hepatic lipidosis
* GLDH horses, cattle, llamas
* Look at ketones
Induced Enzymes (U/L) and where they occur? what do they mark, and what animals?
- ALP – biliary epithelial cells & hepatocyte canalicular surfaces
- GGT – biliary epithelial cells
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* Markers of cholestasis, drug effects, endocrinopathies, bone lysis (ALP)
* Both SA and LA
ALP - what species is it used for? what does it tell us predominantly? what is the timeline? special considerations for cats and LA?
Cat, Dog Horse, Bovine
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Cholestasis
* Liver ALP is predominant isoenzyme
* Induction from cholestasis can be marked
> Can see 4-5x increase in dogs
* Generally takes several days to see increase on biochem
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* Cats – less dramatic increases than dogs
* But important, as T1/2 is short (6h); must be followed up
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* LA – Ref intervals wide, therefore less sensitive (GGT better)
* Horses – may increase with colic
* Works in cattle, but cholestasis less common
ALP - uses other than cholestasis?
Not just cholestasis:
*Endogenous / exogenous corticosteroids > induction in dogs
> Requires 7 d exposure
> “sALP” steroid ALP
> Hyperadrenocorticism – good sensitivity, poor specificity
> Can remain increased weeks to months
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- Anticonvulsant therapy (e.g., phenobarbital) & phenylbutazone
- Hepatic lipidosis / hyperthyroidism in cats
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- ALP is not liver-specific – recall:
- Present in: liver, bone, intestine, kidney, placenta, WBCs
- But T1/2 is shorter for isoenzymes from other sources
is ALP liver specific? what is the difference between liver and other isoenzymes?
- ALP is not liver-specific – recall:
- Present in: liver, bone, intestine, kidney, placenta, WBCs
- But T1/2 is shorter for isoenzymes from other sources
Bone-ALP
(bALP)
- what animals do we see this in? when and why?
Cat, Dog Horse, Bovine
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- Young animals (growing) 2-3x adult value (higher in foals)
- Adult animals – 2-4x increase with:
> Neoplasia involving bone
> Osteomyelitis
> Hyperparathyroidsm
> Hyperthyroidism, etc.
GGT - what animals is this used for? what does it tell us? comparison to ALP?
Cholestasis
* Most GGT is from biliary tree
* More specific for cholestasis than ALP, esp. LA and cats
> (i.e., fewer things cause it to increase, it’s not present in bone, etc.)
* Takes longer to increase than ALP
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* Steroid induction happens in dogs – mild
DDx Increased ALP & GGT? other signs to look for
Cholestasis
> pre, intra, or post hepatic
* Yellow mucous membranes / sclera
* Increased total bilirubin
what drugs can increase ALP in dogs?
Dogs – drug induction:
* Corticosteroids – exogenous / endogenous
* Anticonvulsants / NSAIDs
how long does it take ALP to increase from corticosteroids in dogs? what other enzyme clues may we see?
- 7 d exposure for ALP to increase from corticosteroids
- Oral, parenteral, topical, otic, ophthalmic
- Hyperadrenocorticism
- ± increased ALT
- Corticosteroid ALP (cALP), GGT may also increase
what anticonvulsants / NSAIDs can increase ALP in dogs? how will GGT be affected?
- Phenobarbital, phenytoin, primidone
- Phenylbutazone
- GGT not increased
DDx Increased ALP
- Cats with ↑ ALP but normal bilirubin? what other enzyme clues can we use to piece things together?
- ALP and/or ALT – hyperthyroidism
> 90% of cats with hyperthyroidism will have an increase in one or the other of ALP or ALT - ALP and AST – hepatic lipidosis
DDx Increased ALP - clue we can use to figure out if due to bone lysis?
Look for hypercalcemia
- can sue radiographic evidence as well
- multiple myeloma?
DDx Increased GGT Only
Post colostrum
* Puppies, lambs, calves
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Foals mild increases – not colostral origin
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Acute hepatic injury:
* Membrane fragment release
* Dogs with adverse reaction to anticonvulsant medication
> May see prior to increases in ALT
* Horse & cow with pyrrolizidine alkaloid toxicity
are liver enzymes liver function tests?
NO
Worried about Liver Function? what should we look at?
Look at what the Liver Synthesizes or Processes
&
Perform Liver Function Tests
Substances Synthesized by the Liver? \
what do we expect in liver failure?
- Albumin
- Urea
- Cholesterol
- Coagulation factors
- Glucose
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Expect some or all of these to be decreased in liver failure
Recall: low albumin and high globulins
Always run a coag panel if liver will be sampled!
Substances Metabolized / Removed by the Liver (endogenous)
- Bilirubin
- Cholesterol
- Serum Bile Acids
<><><><><><><> - Serum Ammonia
- Exogenous Ammonia Tolerance Test
Serum Bile Acids - how and where are they made and stored? what do they do?
- Made by liver from cholesterol
- Stored in gall bladder
- Aid in absorption of fat and fat-soluble vitamins
Serum Bile Acids
- efficiency of enterohepatic recirculation in a healthy animal?
- Reabsorbed into blood from GI tract > portal blood
- Healthy animal – very efficiently cleared from portal circulation, secreted into biliary system
When is it Useful to Measure Serum Bile Acids? when should we not?
- When liver enzymes increased but bilirubin normal
> i.e., When suspect, but can’t prove, liver disease
> Don’t do if icteric – increased in any animal with cholestasis; serum bile acids will be decreased because they are in the bile - To monitor liver function in cases of known hepatic disease
Increased Serum Bile Acids - when?
- Deviation of Portal Circulation
* Portosystemic shunt
* Cirrhosis - Decrease in hepatocyte uptake
* Diffuse hepatocellular disease - Decreased bile excretion with subsequent regurgitation into blood
* Hepatic / post-hepatic cholestasis
Interpreting Serum Bile Acid Results – SA threshold for diseasew
CAT
normal (pre-prandial) <15
liver disease (post-prandial) >25
equivocal (post-prandial) 15-25
DOG
normal (pre-prandial) <15
liver disease (post-prandial) >25-30
equivocal (post-prandial) 15-25
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if equivocal, can do abdominal U/S and recheck in a few weeks to see trends in bile acids
Interpreting Serum Bile Acid Results – Horse, Ruminants, Llama
- Usually just a single sample
<><> - Horse – marked increases in SBA 40-100 μmol/L
> Hepatic necrosis, hepatic lipidosis, neoplasia, cirrhosis
<><> - Cattle – a lot of variation – but still best test for detection of hepatobiliary Dz in cattle
Two Major Problems of the Exocrine Pancreas
- Injury
- Insufficiency
Detection of Pancreatitis – Dogs & Cats
- what clues can we see in blood?
- ~50% will have neutrophilia
> because pancreatitis is like a bomb going off in the abdominal cavity, causing a lot of inflammation (body is autodigesting). May have left shift. - May have thrombocytopenia (consider DIC)
> due to inflammation setting off coagulopathy - Hypocalcemia
> Saponification of fat, OR, off food
Detection of Pancreatic Injury
- different methods from the lab
- AHL has DGGR-lipase assay –THE lipase on regular biochemical profile:
* If AHL lipase is increased, no need to run the IDEXX spec PLI
* Not increased by decreased GFR (amylase still is, though)
<><><><> - Serum amylase (should be >5x)
<><><><> - IDEXX – specific Pancreatic Lipase Immunoreactivity (spec PLI)
<><><><> - Peritoneal fluid amylase/lipase
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<><><><> - Trypsin-like Immunoreactivity (TLI) > better for EPI
Detection of Pancreatic Injury in house? best for whay type?
- In-house rapid test SNAP® cPLTM
> Sensitivity 65-82% (depends on severity)
> Specificity >95% - In-house rapid test SNAP® fPLTM
> Sensitivity 54-100% (depends on severity)
> Specificity 91%
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* Work best for moderate-to-severe pancreatitis
Exocrine Pancreatic Insufficiency (EPI)
- whats this? result?
- Inadequate production and secretion of pancreatic enzymes
- Loss of pancreatic acinar cells
- Results in inadequate digestive function (maldigestion)
> Steatorrhea
Exocrine Pancreatic Insufficiency (EPI)
- what test can we do to detect this?
Normal animals – small amount trypsinogen in blood
* There is a ‘normal’ amount of TLI in healthy animals
* If animal has normal TLI it indicates normal pancreatic function
* Too little TLI = exocrine pancreatic insufficiency
Memorizing the Difference between PLI and TLI
- PLI = pancreatitis in dogs and cats
> P for pancreatitis - TLI = Exocrine Pancreatic Insufficiency (EPI) in dogs and cats
> T for toilet paper (EPI) (steatorrhea)
A dog has an increase in bilirubin. Which of the following enzymes will be most markedly increased? Select all that apply.
A. ALP
B. ALT
C. AST
D. CK
E. GGT
F. GLDH
A. ALP
E. GGT
> induction enzymes
An older dog has an increase in ALP and calcium. What is the most likely cause of these increases?
A. Osteosarcoma
B. Bone growth
C. Cholestasis
D. Immune-mediated hemolytic anemia
A. Osteosarcoma
An 11-year-old cat presents for a wellness exam. The cat has a mild increase in ALP and ALT. What test would you run next?
A. Abdominal ultrasound to look at liver echotexture
B. Radiographs to look for a lytic bone lesion
C. Thyroid hormone measurement
D. Look for yellow mucous membranes
C. Thyroid hormone measurement
– Yes, 90% of cats with hyperthyroidism will have an increase in one or the other of ALP or ALT
Which of the following are indicators of liver function? Select all that apply.
A. Albumin
B. Serum bile acids
C. Bilirubin
D. ALT
E. Lipase
F. Cholesterol
A. Albumin
B. Serum bile acids
F. Cholesterol
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C. Bilirubin – this is made by the liver but is not considered evidence of liver’s synthetic capacity (animals with liver failure can have normal bilirubin because of the imbalance between not making it and not excreting it)
D. ALT – no, gives evidence of hepatocellular damage, not synthetic capacity
A horse has acutely increased GLDH, but bilirubin is within the reference interval (normal). What is or are reasonable next test(s) to perform? Select all that apply.
A. Serum bile acids
B. Liver ultrasound
C. Liver biopsy
A. Serum bile acids – yes, this is a good choice when there is no cholestasis but liver disease is suspected
B. Liver ultrasound – yes
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C. Liver biopsy – no, need to wait to see if it’s chronic
A dog presents with foul smelling diarrhea and weight loss. Serum TLI (trypsin-like immunoreactivity) is within the reference interval. What is the most likely diagnosis?
A. Pancreatitis
B. Liver failure
C. Exocrine pancreatic insufficiency
D. Small intestinal bacterial overgrowth
D. Small intestinal bacterial overgrowth
– yes, because this is the next most likely differential diagnosis for smelly diarrhea in an animal with ill thrift
