Liver function tests and interpretation

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Liver Function Tests

Liver Function TestsDr.S.Sethupathy, M.D,Ph.D,Professor &Head, Dept.of Biochemistry,RMMC, AU

Battery of tests Liver function tests are useful for the diagnosis assessment of prognosis monitoring of liver diseases. Liver carries out diverse functions So a battery of tests are needed.

Liver functions

1. Excretory functionLiver is involved in the uptake, conjugation and excretion of bilirubin derived from degradation of heme in reticuloendothelial system. The conjugated bilirubin is excreted via bile. Liver also detoxifies ammonia, drug metabolites and xenobiotics.

2.Metabolic functionscarbohydrate metabolism- glycogen metabolism, gluconeogenesis, blood glucose maintenance.Lipid metabolismCholesterol metabolism, bile acid synthesis, metabolism of lipoproteins, VLDL synthesis, synthesis of triacyglycerol .Protein metabolismCatabolism of proteins, synthesis of non- essential amino acids, formation of urea from ammonia

3 . Synthesis of plasma proteinsLiver synthesizes albumin, coagulation factors such as prothrombin. 4. Storage functionVitamin A, D, K, B12 , Iron as Ferritin are stored in liver.

Serum EnzymesSerum enzymesIn liver cell damage, liver tissue enzymes leak into circulation and their levels are increased in plasma.Aspartate transaminase (AST)Alanine transaminase (ALT)Alkaline phosphatase(ALP)Gamma glutamyl transpeptidase (GGT)

Bilirubin metabolism

Heme is degraded in reticuloendothelial system Iron is reutilized. Globin protein catabolized into amino acidsThe bilirubin is formed from porphyrin ring of heme which is water insoluble It is called unconjugated bilirubin. Unconjugated bilirubin is transported by albumin to liver.

Role of liverIt is involved in the uptake of unconjugated bilirubin and conjugates them to bilirubin diglucuronide by the enzyme UDP-glucuronyl transferase using UDP- glucuronic acid, the active donor of glucuronyl units. The conjugated bilirubin is water soluble and excreted in bile.

In the intestine- Conjugated bilirubin gets deconjugated by bacterial beta-glucuronidase enzyme in the terminal ileum and large intestine. The pigment is further reduced by fecal flora to a group of colorless, tetra pyrrolic compounds known as urobilinogens. A small fraction of urobilinogens is absorbed in the terminal ileum and re-excreted by liver. This is called enterohepatic circulation.

Then some of the urobilinogens being water soluble, escape into urine normally. In the intestine, further reduction of urobilinogens form stercobilinogen which is excreted in feces. Some Urobilinogen gets back to liver and reexcreted into intestine via bile . This is enterohepatic circulation.Oxidized products form urobilin and stercobilin which are yellow colored.

Jaundice is the yellowish discoloration of skin , mucous membrane and sclera. It is due to hyperbilirubinemia. Normal serum bilirubin level is 0.2 - 1 mg/dl.Hyperbilirubinemia may be of conjugated or unconjugated or both. Normal serum unconjugated bilirubin level is 0.2-0.8 mg/dl and conjugated bilirubin level is 0.2-0.4 mg/dl. Jaundice clinically appears when the serum bilirubin level goes beyond 3 mg/dl.

Vanden bergh test

Bilirubin reacts with diazotized sulfanilic acid to form purple colored complex azobilirubin. Conjugated bilirubin gives color in aqueous medium immediately and is direct positive.Unconjugated bilirubin, in methanol only color develops and is indirect positive. If both fractions are there, the color developed in aqueous medium deepens on adding methanol and is called biphasic.Van den Bergh test is indirect positive in hemolytic jaundice, direct positive in obstructive jaundice and biphasic in hepatic jaundice.

Hemolytic JaundiceHemolytic jaundice or pre-hepatic jaundice or unconjugated hyperbilirubinemiaInvestigations Serum unconjugated bilirubin is increased. Urine bile salts and bile pigments will be negative. So it is called as acholuric jaundice.Urine urobilinogen will be excess.Motion is high colored (dark brown).CausesHemolytic anemia, hemoglobinopathies, mismatched blood transfusion.

Inborn errorsGilbets syndrome (GS): is the most common hereditary cause of increased bilirubin characterized by elevated levels of unconjugated bilirubin in the bloodstream. Enzyme glucuronyltransferase deficiency.Crigler Najjar syndrome: It is a rare , AR disorder with high levels of unconjugated hyperbilirubinemia affecting brain. UDP- glucuronyl transferase enzyme is defective.

Obstructive jaundice or post hepatic jaundice or conjugated hyperbilirubinemiaSerum conjugated bilirubin is increased. Urine bile salts, bile pigments will be positive. Urine urobilinogen will be less or absent. Motion is clay colored.CausesBiliary duct obstruction - due to gall stones, tumor in the bile duct, carcinoma head of pancreas, lymph node enlargement in porta hepatis,

Inborn errorsDubin Johnson syndrome : AR disorder Increase of conjugated bilirubin in the serum without elevation of liver enzymes (ALT, AST). Defective secretion of conjugated bilirubin into the bile. Liver cell are pigmented.Rotor syndrome . Rare , AR disorder with increase in conjugated bilirubinsimilar to Dubin Johnson syndrome except that the liver cells are not pigmented.

Hepatic jaundiceBoth unconjugated and conjugated bilirubin levels are increased in serum.Urine bile salts, bile pigments are positive.Urine urobilinogen is lesser than normal amounts.Motion is pale yellow colored.Causes Alcoholic hepatitis, viral hepatitis, drug induced intra hepatic cholestasis.

Tests based on synthesis of plasma proteinsSerum albumin level - half- life is 20 days.In liver cirrhosis, albumin level is decreased. Normal serum albumin level is 3.5-4.5 gm/dl and globulin level is 2.5-3.5 gm/dl. Normal albumin globulin ratio (AG ratio) is 1.2 to 1.8 :1 . In cirrhosis, AG ratio is reversedSerum globulins are increased in chronic active hepatitis and cirrhosis of liver.

Prothrombin timeNormal 10-14 secs. In liver dysfunction, it is prolonged. It is not recovered by Vitamin K administration. In vitamin K deficiency due to obstructive jaundice also, there will be prolonged prothrombin time But that will recover after parenteral administration of vitamin K.

Tumor marker- -feto protein (AFP) is elevated in hepatocellular carcinoma.Ceruloplasmin Its level is decreased in Wilsons disease.Serum protein electrophoresisIn cirrhosis of liver, albumin is decreased and gamma globulins are increased. In biliary obstruction, 2 and 2 globulins are increased.

Serum enzymesHepatocellular damageSerum amino transferases- Aspartate amino transferase (AST) and Alanine amino transferase (ALT) are elevated. Normally both are lesser than 40 U/L.In acute hepatitis, may increase to more than 1000 U/L.ALT is found in cytosol and is more liver specific. AST/ALT ratio is lesser than 1. But in alcoholic hepatitis, AST is increased more than ALT and the ratio is more than 2. This is due to release of AST from mitochondria.

Obstructive liver diseaseSerum alkaline phosphatase (ALP) level is increased in case of cholestasis, hepatic carcinoma and biliary tract obstruction. ALP is present in bone, liver, intestine and placenta. In the absence of bone disease or pregnancy, ALP elevation indicates cholestasis. Gamma glutamyl transferase (-GT) level is increased in obstructive jaundice. Its level is a sensitive biomarker of alcohol abuse or alcoholic liver disease.5-nucleotidase enzyme is increased in hepatobiliary disease.

Blood ammoniaIt is increased in severe hepatocellular damage either acute or chronic. Normal blood ammonia level - 15- 60 g/dl.Serum bile acidsThey are increased in liver disease with cholestasis.

Bromosulphathalein (BSP) excretion testBSP dye (5mg/kg, 5% w/v solution ) given by intravenous route is rapidly removed by liver and excreted in bile. Normally 95% of dye is cleared within 45 minutes only less than 5% of dye is found in blood after 45 min. In hepatic dysfunction, it is more than 5%. Higher level of dye after 2 hours than at 45 min due to secondary rise is diagnostic of Dubin Johnson syndrome.

Physiological Classification Blood Bili-Alb decreased uptake Gilbert syndromeHepatocyte Bilidecreased conjugationNeonatal JUDP-Glu.aToxic J Chloroform, CCl4, paraCrigler-Najjar syndromeGilbert syndrome.Bilirubin Diglucuronide

decreased secretion Dubin- Johnson syndrome.Rotor synd.

Bileduct Bilirubin Diglucuronide

UnconjugatedConjugatedHemolytic anemiaObstruction of biliary treePhysiological jaundiceDubin-Johnson syndromeCrigler-Najjar syndrome type I & IIRotor syndromeGilbert syndromeHepatitis (Both)-conj and unconjToxic hyperbilirubinemia

Flow Chart - JaundiceJ (suspected)

HistoryClinical examinationVD Berg testSr.Bili. Total/Difference (CHB/UCHB)Total Bili. Increased Total bili. Increased UCHB increased CHB increased VD Berg test VD Berg test (indirect +ve) Direct +veHemo Jaundice Obst. J. + HC.J

Obst. J+ HC.JSr.ALP (Crucial test)