Tests for hepatic & pancreatic function & integrity

What physiological factors can you test in the liver in general?

• Hepatocellular injury

  • Leakage of enzymes from damaged hepatocytes

• Cholestasis

  • Reduced bile excretion- induction of synthesis of enzymes

• Hepatic function

  • Decr prod / catabolism of substances

• Hepatic portal circ

  • Decr extraction of substances absorbed in intestine

Where are liver enzymes primarily located?

Inside the cells

When does the activity of the enzyme in serum incr?

When rate of enzyme entering blood exceeds rate of inactivation / removal

How is enzyme measurement expressed?

International unit of enzyme activity (IU) = amount that catalyses conversion of 1µmol of subtrate per min

What are liver leakage enzmes indicative of?

Hepatocellular damage

• They fluctuate in chronic hepatitis / hepatopathy

• Declining trend indicates either improvement or potentially reduction in liver mass

What 'leakage enzymes' are routinely measured and what is the difference between them?

• ALT (alanine aminotransferase)

  • Liver specific but may incr w/ severe m. damage (e.g. rhabdomyolysis)

  • more clinically significant in cats due to shorter half life cf to dogs

• AST (aspartate aminotransferase)

  • Not so liver specific as found in liver, muscle and RBCs

Shorter half life in cats cf to dogs for both

Some others: LDH (not liver specific), GLDH (liver specific, useful in large animals) , SDH (liver specific but unstable, can't measure in serum)

What are liver induction enzymes?

Enzyme production via modifications in physiological processes like transcription & translation

Induction triggered by endogenous substances like bile acids / exogenous substances e.g. drugs

What is the activity of induction enzymes increased by?

• Cholestasis

  • Bile acid accum in hepatocytes incr enzyme prod

• Some drugs

  • E.g. glucocorticoids & phenobarb

What are the liver 'induction' enzymes that you can measure?

• ALP

• GGT

What are the two isoenzymes of ALP?

Intestinal-ALP

Tissue non specific

• Bone ALP

• Liver ALP

• Corticosteroid ALP (unique to dogs)

Compare ALP diagnostic value in dogs vs cats

• More sens for cholestasis in dogs

• More specific for cholestasis in cats

What are the main causes of incr ALP?

• Cholestasis

• Drugs

  • Glucocorticoids (only dogs)

  • Phenobarb (mostly dogs, only minimally sporadic incr. in cats)

• Bone lesions

• Mammary neoplasms

In what organs is GGT present in the highest conc.?

• Kidney, pancreas, liver

  • Only liver GGT contributes to serum

  • Kidney & pancreas lost in urine & pancreatic secretions

How does GGT importance differ between species?

Preferred over ALP to detect cholestasis in horse, ruminants, birds & poss cats

What should be measured in dogs vs cats if you cannot measure both ALP & GGT together?

ALP in dogs

GGT in cats

What can cause an incr. GGT?

• Cholestasis (biliary hyperplasia)

• Drugs (only dogs)

  • Glucocorticoids, phenobarb

• Colostrum ingestion

How can we differentiate between cholestasis & drugs causing an incr in liver enzymes?

ALP>GGT = probably drug if disproportionately higher

GGT> ALP = unlikely to be drug

What are the different causes of hyperbilirubinaemia?

Prehepatic = 2° to haemolysis

• Check for anaemia

Hepatic = decr bilirubin uptake, conjugation & excretion (liver dysfunction —> intrahepatic cholestasis)

Posthepatic —> 2° to obstruction of extrahepatic bile duct

With a post hepatic hyperbilirubinaemia, other than incr bilirubin what else can confirm this?

• Often cholestatic enzymes (ALP & GGT) much higher than leakage enzymes (ALT & AST)

• Serum cholesterol often high

• U/S very helpful

What aetiology causes hyperbilirubinaemia?

• Haemolysis

• Obstructive cholestasis

• Functional cholestasis (sepsis)

• Liver insufficiency

• Fasting/ anorexia (mostly in horses, minimal in dogs & cats and only if prolonged)

How is bilirubin measured?

Total or conjugated

• Conjugated = direct

• Unconjugated = can be calculated

  • (total bilirubin - direct bilirubin)

What is the diagnostic value of measuirng both direct and indirect BIL?

• Not generally useful for cause of hyperbilirubinaemia

  • Exception is horses w/ fasting hyperbilirubinaemia (mostly due to indirect BIL)

How can you test liver function?

• Decr uptake & excretion

  • Incr bilirubin & bile acids

• Decr syntehsis (bc prod by liver)

  • Decr Albumin, glucose, cholesterol, coagulation factors & inhibitors

• Decr conversion

  • Incr ammonium (ammonia)

How can you measure alterations in portal circulation?

• Incr bile acids due to decr. uptake & excretion of bile acids

• Incr ammonia due to decr. conversion of ammonia to urea

What are the general features of bile acids?

• Produced in hepatocytes

• Excreted into bile then back into intestine

• Only 10% excreted in faeces, 90% reabsorbed, then 95% goes back to liver & only 5% goes back into systemic circulation

How can you measure bile acids dynamically?

Bile acid stimulation test

• Fasting sample (12hrs fast) —> baseline amount that escapes enterohepatic ciruclation

• 2nd sample 2 hours after giving small meal containing protein & fat

What are the possible causes of an incr. in bile acids?

• Hepatic dysfunction (can't uptake bile acids)

• Cholestasis (Decr excretion)

• Decr portal blood flow

• Postprandial (after meal = normal to see incr.)

When is there no point in measuring bile acids?

If there is hyperbilirubinaemia → cholestasis = cause of incr. bile acid conc.

How do you need take a blood sample for ammonia?

EDTA or heparin plasma:

• Must be harvested immediately after collection & measured within 30-60 mins w/ minimal exposure to air

• If not processed properly —> ammonia may wrongly incr. / decr.

Why does ammonia increase in liver dysfunction?

• In urea cycle liver converts ammonia → urea

• If liver dysfunctioning this does not happen

What causes inc ammonia?

• Hepatic dysfunction

• Decr portal flow

• Post prandial

What secondary hepatopathies can also cause incr liver enzymes?

• Endocrinopathies —> diabetes , Cushings, hyperthyroidism (cats)

• Reactive (pancreatitis, enteritis, systemic inflam)

• Hypoxia (e.g. severe anaemia)

Incr typically mild (less than 5x upper ref limit)

Bile acids usually normal (or mild incr)

What haematological findings are ass. w/ liver dx?

• transferrin = transfers iron

• coag factors produced by liver

  • prolonged PT & PTT

Summarise the typical clinical biochem values look like in liver dx

What are the typical findings of urinalysis in liver dx?

B

C

D

D

What tests can you do for exocrine pancreas integrity? (detects pancreatitis)

• Amylase (not actually recommended for pancreatitis)

• Lipase

Markers of injury to pancreatic cells (diagnosis cannot be made solely on this due to sens & spec of test) —> correlate w/ clin signs, imaging findings, cytology, histopath

Where are amylase & lipase excreted?

Kidneys —> so can incr due to decr GFR

(amylase better in dogs than in cats, but generally not v. useful —> if pancreatitis suspected, don’t measure amylase)

With an incr amylase & lipase activity what are the major causes?

• Pancreatic inflam (pancreatitis)

• Renal dx (mild, up to x3-4)

• Liver & intestinal dx (only amylase, minimal/mild incr.)

• Glucocorticoids (only lipase, mild up to x2)

What are some more specific assays used to measure lipase (more specific than traditional assay)?

(Traditional assay not specific enough)

• DGGR lipase (more specific to pancreatitis)

  • spec depends on applied cut-off value → sent to ext. lab to test

  • can be incr. because of renal dx / glucocorticoid admin

• PLI (aka specific pancreatic lipase) —> best test for pancreatitis but £££ & sent to ext. lab (equiv. SNAP test for in-house)

  

How is canine specific PL test interpretted?

What other lab findings are supportive of pancreatitis?

• damage of beta cells of pancreas → diabetes mellitus

What is the test of choice for exocrine pancreatic insufficiency (EPI)?

Trypsin-like immunoreactivity

• Detects trypsinogen, trypsin & trypsin bound to protease inhibitors

• Species-specific assays required

• Highly sens & spec test for diag EPI → decr. TLI

• Incr. TLI has poorer performance cf. PLI for pancreatitis

How is canine TLI interpretted?

A+B

D

DO NOT test for amylase / lipase if pancreatitis suspected

Case 1:

• Hx: anorexia, lethargy, acute vomiting

• Physical examination: quiet, pain on abdominal palpation

USG = 1.042

• Mod neutrophilia w/ band neutrophils (L shift), mild monocytosis, mod thrombocytopenia

  • changes in leukogram → acute / active inflam

  • genuine thrombocytopenia —> no platelet clumping on blood smear, incr. consumption/destruction / decr. production?

• Further tests due to genuine thrombocytopenia:

  • prolonged PT & PTT, incr. D dimers, decr. ATIII = DIC (disseminated intravascular coag)

• Mild incr ALP, ALT, incr cholesterol, creatinine & urea, incr P, incr DGGR lipase

  • Marked DGGR incr → pancreatitis

  • Incr ALT, ALP & cholesterol → hepatocellular injury & cholestasis → 2° reactive hepatitis probs

• USG = Prerenal azotaemia (due to decr. GFR → dehydration)

  • urine well conc. = pre-renal

  • incr. P, urea & creatinine

Imaging / cytology of pancreas probably next step

Case 2:

10yo MN Lab

Hx: weight loss, lethargy, PUPD

CE: quiet, fluid thrill on abdo palp

Discuss & what further test would you do here?

• Mild incr ALP, ALT incr

  • ALT incr = hepatocellular damage only (nothing to do with liver dysfunction)

  • ALP incr = cholestasis

• Low cholesterol, Ca, Urea, albumin

  • Liver dysfunction

• Further tests —> bile acids + cytology of liver to investigate hepatopathy

  • Incr. bile acids so chronic hepatitis

  • mild lipidosis