Liver Function Tests Flashcards
Function of the liver
Are AST and ALT liver function tests?
No, these enzymes can be normal while liver function is impaired
Three categories of liver function tests and what they measure
cholestatic, hepatocellular injury and hepatic synthesis impairment. One is associated with obstruction of the biliary tree (most often by a gallstone) that causes decreased bile excretion - we will call this lab pattern cholestatic. Hepatocellular injury is associated with damaged hepatocytes from ischemia, toxins or viruses). Synthetic dysfunction can be indirectly estimated by several tests that concern products of the liver and may be caused by acute or chronic liver injury.
Indications of Cholestasis
Cholestasis presents with an elevation of serum alkaline phosphatase and maybe bilirubin levels, approximately half of which is conjugated. It can be from anything that would block the flow of bile (commonly a gallstone in the common bile duct - known as choledocholithiasis). AST/ALT may also be elevated.
Hepatocellular injury indiciation
Hepatocellular injury is indicated by elevation of AST/ALT (aka transaminitis). It may occur from cholestasis (and in that case alk phos and bilirubin would also be abnormal) but is often seen alone with non-alcoholic fatty liver disease, viral or other insults.
When would you see combination of both cholestasis and hepatocellular injury
when the liver is diffusely injured: acute ischemia (sometimes called shock liver) or toxin-ingestion.
Non-hepatic causes of abnormal liver tests
What are the transaminases
Aspartate transaminase = AST
occasionally mentioned as SGOT
Alanine transaminase = ALT
occasionally mentioned as SGPT
Where else are transaminases found
cardiac muscle, skeletal muscle, kidney, brain, pancrease, lung, leukocytes, erythrocytes.
AST/ALT ratio > 2-3
AST is more commonly associated with alcohol-induced liver damage. When looking at the AST/ALT ratio, the classic proportion is AST 2-3 times highter than ALT when associated with alcohol as a cause
AST/ALT < 1
AST/ALT < 1 is likely in chronic viral hepatitis.
AST/ALT close to one
AST/ALT close to one is consistent with non-alcoholic steatotic hepatitis (NASH or fatty liver)
Levels of transaminase elevation and indication
Very mild elevation (up to 300) can be from slight injury (like a good workout).
> 1,000 U/L is most commonly from a viral hepatitis, toxin or drug-induced liver injury
>10,000 or the very highest is most likely from ischemic hepatitis, often in the setting of severe hypovolemia, sepsis or congestive heart failure-related ischemia.
What is Alkaline Phosphatase, and how to differentiate for liver
Group of isoenzymes distributed widely throughout the body (typically liver and bone).
The isoenzymes can be isolated to further determine the source of: intestinal, non-specific, placental, placental-like
These isoenzymes can be ordered, but a quicker, cheaper test to investigate whether elevated AlkP is of liver origin is GGT to see if it is associated with a hepatic cause.
Causes of Alk Phos elevation
This can be elevated during normal growth spurts in children or from placental development in the third trimester of pregnancy.
If this is all that’s elevated, it may be from a blockage like partial bile duct obstruction, infiltration (primary biliary cirrhosiss) or focal liver mass.
If it’s elevated along with bilirubin, and/or a mild elevated of transaminases, consider a process causing intrahepatic or extrahepatic cholestasis.
Causes of Indirect Hyperbilirubinemia
What is a MELD score
This MELD score (model for end-stage liver disease) is a predictor of 5 year mortality that was initially used for liver-transplant but is now extrapolated into 5-year survival likelihood.
Dont need to know formula
Normal values
