Liver Function Tests PDF

Liver Function Tests Clinical chemistry Dr.Balsam Alkassar Lec 3 Liver function tests LFT are different tests can give different information about hepatic function or dyfunction. Also can be defined as blood tests that measure liver enzymes and proteins in the blood. Enzyme test...

Liver Function Tests Clinical chemistry Dr.Balsam Alkassar Lec 3 Liver function tests LFT are different tests can give different information about hepatic function or dyfunction. Also can be defined as blood tests that measure liver enzymes and proteins in the blood. Enzyme tests show the extent of damage to a liver, while proteins show how well a liver is performing. LFT is a diagnostic tool used to detect liver damage also used to measure the severity and type of liver disease. Standard liver panel: A. Liver enzyme tests measure levels of: 1.Alanine-transaminase(ALT)found in liver tissue only so it is a specific test for liver damage. 2.Aspartate- transaminase (AST) larger amount and found in cytoplasm of hepatocyte so elevate early and more sensitive BUT less specific. 3. A plasma AST:ALT ratio of > 2 is suggestive but not diagnostic of alcoholic liver disease and a ratio < 1 suggests chronic viral hepatitis or hepatic steatosis. 4.Alkaline phosphatase (ALP) elevated in biliary duct defects with GGT because ALP synthesis is increased and the enzyme within the biliary tract is regurgitated into plasma. If AKP only elevate ,bone disease more suspected because it found in osteoblast. 5.Gamma-glutamyl-transpeptidase(GGT) derived from the endoplasmic reticulum of the cells of the hepatobiliary tract. GGT is often measured relative to another enzyme, alkaline phosphatase (ALP). If GGT and ALP are both elevated, doctors will suspect the patient have problems in the bile ducts. As a summary, Increased levels of ALT and AST can be a sign of liver damage, while increased levels of ALP and GGT can be a sign of bile duct damage. B. Liver protein tests measure: 1.Total protein, which consists of measuring levels of globulin, prothrombin and albumin. 2.Albumin: decrease in chronic liver disease causing edema and ascites. 3.Prothrombin time: prolonged PT with normal vitamin K level mean liver disease due to clotting factors deficiency. In another words, in liver cirrhosis mainly impairs albumin and prothrombin synthesis.  As we mentioned in last lecture globulin aids the immune system with fighting infections, prothrombin aids in blood clotting, and albumin levels show whether the liver is producing a normal level of proteins. C. Bilirubin levels (total bilirubin = unconj + conj) indicate the excretory function of liver. During advanced stages of liver damage or due to excessive destruction of RBC defect in (conjugation function) so unconjugated bilirubin can leak out of the liver and cause jaundice, turning the urine dark, pale stool and eyes yellow. While if the defect in biliary system example in case of cholestasis increase conjugated bilirubin because of back pressure from bile duct obstruction. unconjugated liver damage +conjugated (RBC hemolysis ) conjugated + ALP defect in biliary system GGT + ALP defect in biliary system GGT alcoholic toxicity, drug toxicity, toxins