Liver Function Tests Flashcards
Physical Exam indicators of Liver abnormalities
Jaundice Abdominal pain and fever Stigmata of chronic cirrhosis Ascites GI bleeding
Liver function tests Include…
Excretory function - serum bilirubin
Enzyme Levels - AST, ALT, ALP, GGT
Synthetic Functions - Serum Albumin, Clotting factors, AFP
Metabolic functions - Serum Ammonia, Blood glucose
Serum Bilirubin
Liver conjugates bilirubin with glucuronic acid to form conjugated bilirubin, that is excreted into the intestine
Serum bilirubin is seen in hepatocellular disease which results in lower capacity to uptake and conjugate bilirubin
Also seen in hepatitis (inflammation) and Cholestasis (obstruction)
Intra- vs Extra- Hepatic Cholestasis
Intrahepatic - Inflammation and destruction of hepatocytes due to virus or drug toxicity compressing on the bile duct due to cirrhosis
Extrahepatic - Gall stones or tumors in the common bile duct. Tumors of the head of the pancreas
Enzyme finding in Hepatocellular Injury
ALT and AST are raised in viral and drug induced hepatitis as well as long standing obstructive Jaundice
ALT is more specific for acute liver damage than AST. ALT»>AST
AST»>ALT in long standing Alcoholic Cirrhosis 2:1 ratio
Enzyme findings in Cholestasis
Alkaline Phosphate (ALP)
- Secreated by biliary cannaliculi.
- intra or extra hepatic obstruction results in elevated ALP
(also seen in pregnancy, growing children, and bone disease)
Gamma glutamyl Transferase (GGT)
- Secreted by biliary ducts
- synthesis is induced by alcohol
(GGT estimation can be performed to differentiate the hepatic and the non-hepatic (alcohol consumption) causes of raised ALP)
Serum Albumin in liver function determination
-Long standing (chronic) liver disease is characterized by low serum albumin levels
Hypoalbuminemia contributes to the development of ascites and pedal edema
Low serum albumin levels also affects binding of hormones, ions like calcium and drugs to albumin
-A decrease in Albumin with an increase in gamma globulins usually indicates cirrhosis
Clotting factors in liver function determination
Liver synthesizes clotting factors V, VII, IX, X, prothrombin(II) and fibrinogen(I)
Increased prothrombin time indicates deficiency of clotting factors synthesized by the liver
Prothrombin time may also be elevated in cholestasis which results in deficient absorption of vitamin K
The liver is involved in vitamin K activation. (dependent clotting factors II, VII, IX, X)
(accompanying finding in hepatocellular damage)
Blood Glucose in metabolic function of the liver
Chronic liver disease can alter blood glucose level and impair the ability of liver to maintain blood glucose levels
Blood Ammonia Levels in metabolic function of the liver
Increased blood ammonia levels may indicate fulminant or end-stage liver disease (impairment of the urea cycle)
(Elevated blood ammonia levels are contributory to the development of hepatic encephalopathy and altered consciousness in patients with end stage liver disease)
Lipid Metabolism in metabolic function determination of the liver
‘Fatty liver’ is a pathological condition in which there is excessive deposition of triacylglycerol in liver
Damage to hepatocytes by ethanol results in fatty liver:
- Decreased beta oxidation due to increased NADH
- Increased FA synthesis due to increased acetyl CoA
- Decreased rates of VLDL secretion by liver, due to the hepatotoxic action of ethanol
Special tests for evaluation of liver function
- Serum alpha fetoprotein - tumor marker
- Serum Iron - hemochromatosis
- Serum Ceruloplasm - Wilson’s Disease (Cu accumulation)
- Serum Alpha1 antitrypsin - Alpha1 antitrypsin deficiency
When to use LFTs
Evaluate severity of Jaundice
Assess viral damage to hepatocytes
Establish if acute or chronic disorder
Assess metabolic function
Monitor drug therapy of hepatotoxic drugs
