Liver Function Tests Study Guide PDF

- Liver Function Tests - LFTs do not measure specific liver function - "especially ALT/AST" - Abnormalities are seen **LATE** in hepatic disease processes - Abnormalities reflect hepatocellular injury more than liver function (AST, ALT) - LFT...

- Liver Function Tests - LFTs do not measure specific liver function - "especially ALT/AST" - Abnormalities are seen **LATE** in hepatic disease processes - Abnormalities reflect hepatocellular injury more than liver function (AST, ALT) - LFTs can help define type of pathology **when combined with clinical assessment**: - Synthetic Function - how well is the liver making what it is supposed to - PT - measures the activity of fibrinogen, prothrombin, and factors V, VII and X - Normal 11-14s - Albumin - Used to evaluate chronic liver disease and hepatocellular function (protein synthesis) - \< 2.5-3 g/dL generally indicates a more chronic problem - Poor specificity (low levels seen with malnutrition, renal losses, 3^rd^ spacing) - INR, Serum Cholesterol, Plasma Pseudocholinesterase (Schless says this, Apex didn't) - INR - Prolonged INR usually indicates liver dysfunction - Effect on coagulation depends on balance between coagulation and anticoagulation factors - Hepatocellular Injury / hepatic cellular integrity - - Aminotransferases: AST and ALT - Serum alanine aminotransferase (ALT): primarily in liver - Aspartate aminotransferase (AST): liver and non-hepatic tissues - Isolated ALT - non-liver sources (heart, skeletal muscle, brain, kidney, pancreas, adipose tissue, blood) - Mild elevation: any hepatocyte injury (fatty liver, infection) - Large elevations: massive hepatic necrosis, fulminant viral hepatitis, drug-induced liver injury, shock liver - Ratio of AST/ALT: may help differentiate alcoholic liver disease (AST that is 2-3x \> ALT) - Lactate Dehydrogenase (LDH): - "tylenol overdose is the most common cause of acute liver failure" - Nonspecific marker of hepatic injury - Extreme elevations seen with ischemia or drug-induced hepatotoxicity (acetaminophen OD) - along with AST/ALT - Extrahepatic disorders can increase LDH (hemolysis, rhabdomyolysis, tumor necrosis, renal infarction, acute stroke) - Glutathione-S-Transferase (GST): - Sensitive for liver injury → short half-life and rises quickly with liver injury - Can also be used as marker for improvement - Cholestatic Disorders: - Hepatic Clearance - - Bilirubin - comes from the breakdown of hgb - Indicates excretory function of the liver - Normal total bilirubin is \< 1.5 mg/dL - Jaundice is usually evident if total bilirubin is \> 3 \*\* repeated 2x - Direct bilirubin → conjugated - water soluble / elevated with bile duct stone or obstruction - Indirect bilirubin → unconjugated - lipid soluble / hemolysis or cirrhosis - Biliary Duct Obstruction - - Alkaline Phosphatase (AP) - Mild elevations may be normal - **Nonspecific** (found in extrahepatic tissues) - Values 2-4x normal seen in cholestatic disease - Can indicate intrahepatic or extrahepatic biliary obstruction - Y Glutamyl Transpeptidase (GTTP) - 5' - Nucleotidase (5'-NT) - In liver failure, improving values may not mean improvement → could mean that there are no more functioning hepatocytes