Laboratory diagnostics of liver disease Flashcards
Name 4 enzymes used to indicate hepatocellular damage
ALT, AST, SDH, GLDH.
These are leaked directly from hepatocytes and indicate damage/necrosis of these cells
Does a blebosome indicate reversible or irreversible damage?
Reversible damage
What is ALT most commonly used for? Describe its rate of increase/decrease
dogs and cats.
Will increase within 12 hours of injury, peaks at 1-2 days and decreased over the next 2-3 weeks.
Is ALT used in large animals?
No - hepatic ALT activity i n large animals is very low so use SDH or GLDH. GLDH is considered liver specific but assays for use in small animals are rarely available.
What should you check if AST is increased?
Look at CK to determine if liver or mm problem is the underlying cause
Describe how CK levels change after injury.
It will increase within 1-2 hours of mm injury, peak at 6-12 hours and decrease over next 24-48 hours. If persistently elevated indicates ongoing damage. AST and ALT will increase more slowly
Define cholestasis. Which enzymes indicate this?
obstruction of bile flow with regurgitation of biliary substances into the blood. Enzymes = ALP and GGT
Where does ALP come from?
bile duct epithelium. increases with cholestasis. also found in boune so increased in young growing animals. Steroid induced isoform in dogs only not cats (so any increase in this species is significant).
Where is GGT derived from?
bile duct epithelium. also found in renal tubular cells so could be found in urine (not blood) if renal tubular damage is present
What is GGT used for?
it is a more sensitive indicator of cholestasis in large animals - ALP has a very wide range
Where can GGT be found in relation to neonates?
in the colostrum so will be increased in nursing animals
Measures of hepatic function - 7
bilirubin, albumin, urea, glucose, cholesterol, ammonia, bile acids
Describe bilirubin metabolism.
bilirubin is a RBC breakdown molecule, it is not water soluble, therefore it needs a carrier molecule (albumin) so it forms conjugated albumin in the liver. This is converted into urobilinogen (enters GIT) and is excreted in urine but some enters enterohepatic circulation (gives yellow colour to plasma). Stercobilinogen is found in GIT and is excreted in faeces.
How does fasting in horses affect bilirubun levels?
fasting for 24 hours or more will produce an increase in bilirubin
When might you see bilirubinaemia? 2
haemolysis and choelstasis
Describe bilirubinuria - normal?
low levels of bilirubin can be found normally in dog urine. Canine renal tubular epithelium can conjugate bilirubin.
Bilirubinuria in the cat is not normal and is always a significant finding. This may be present before elevation of bilirubin levels are detected in the plasma.
What are ammonia and urea both products of?
protein metabolism
How much urea passes back into the GIT and how much is renally excreted?
25% to gut. 75% to renal excretion.
What should you do if urea is increased in the blood test?
Check urine for kidney problem - urea is used primarily to evaluate the renal system as its main route of excretion is via the kidneys.
What should you do if urea if found to be decreased in the blood?
Check the liver (major loss of function is indicated by this clinical sign). This is associated with decreased synthesis.
If ammonia levels are increased, what might you see? What should you do?
ammonium biurate crystals in the urine. run an ammonia tolerance test.
What does the ammonia tolerance test measure?
the liver’s ability to maintain normal blood levels of ammonia both at rest and in response to challenge (an assessment of hepatic function)
Is glucose a sensitive indicator of hepatic function?
No - decreases in glucose production only occur with end-stage liver disease and there are other causes of hypoglycaemia (neoplasia and bacterial sepsis)
What might cause hyperglycaemia? 2
stress (mild increase) and DM
