Normal & Abnormal Liver Function Tests Flashcards
Biochemical Tests of Liver Disease
- no easy measure of hepatic clearance or function
- no highly sensitive or specific test for underlying liver disease
- liver is a silent organ associated with often nonspecific symptoms (fatigue)
- all biochemical tests have limitations in prediction function and prognosis
Complications of Liver Disease
- synthetic impairment
- cholestasis-impairment of bile flow
- decreased clearance
- portal hypertension - portal blood is shunted around the liver and not processed by the liver
Biochemical Tests of Liver Disease
“Liver Function Tests”
- often biochemical measures of hepatocellular injury or impairment of bile flow
- true “function” tests are measures of clearance or synthetic function
- few clinically useful hepatic clearance tests - measuring drug clearance (like Lidocaine)
Liver Chemistries
Tests which detect injury: aminotransferases & Alkaline phosphatase
Tests which measure clearance: bilirubin, ammonia
Tests of Synthetic Capacity: clotting factors made by liver, albumin, cholesterol - late complication of severe dysfunction
Aminotransferases
- aspertate aminotransferase (AST)
- alanine aminotransferase (ALT)
- increase associated with cell injury or death
- AST elevation also increased with muscle injury
- ALT more specific for liver injury
- Marked elevations associated with primary hepatocellulary injury
Alkaline Phosphatase
- Enzyme derived from bile ducts
- Correlates with intrahepatic & extrahepatic injury or obstruction
- Level associated with increased synthesis
- 3 important isoenzymes: Gut, Liver, Bone
Cholylglycine
- serum bile salt
- correlates with the degree of cholestasis, intrahepatic or extrahepatic obstruction to bile flow
Gamma Glutamyl Transferase (GGT)
Gamma Glutamyl Transpepidase
- enzyme in many tissues including biliary ductules
- increased with cholestasis, biliary obstruction
- increased w/induction by numerous chemicals (Phenytoid/Dilantin & ethanol)
- many meds & chemicals induce GGT that is limited to clinical utility
- isolated GGT elevation is often due to medications or ethanol
Blirubin
- level represents a balance b/w input & hepatic removal
- imperfect measure of hepatic clearance & excretory function
- inc. w/impaired clearance by the liver
- inc. w/intrahepatic & extrahepatic obstruction
Ammonia
- detoxified in liver by Urea cycle & glutamine synthetase reaction
- in chronic liver disease function & protosystemic shunts around liver
- often, but not perfect correlation w/hepatic encephalopathy
Synthetic Function Tests
- Prothrombin Time: prolonged when factors I, II, V, VII, X deficient or Vit. K deficient, correlates well with hepatic synthetic function
- International Standardize Ration (INR)
- Albumin: T1/2 ~20 days, hepatic synthesis, rapidly changed with acute illness, malnutrition
Child Pugh Score
A is best B in between C is most impaired based on: alb, bili, ascites, enceph, PT/INR Transplant 9-10
Model of End-Stage Liver Disease (MELD)
international normalized ration (INR) - standardized measure of Prothrombin time, hepatic synthetic function
- bilirubin
- creatinine