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• Major Metabolic Functions of the Liver

  • Synthetic Function: Plasma proteins (albumin, globulins), cholesterol, triglycerides and lipoproteins
  • Detoxification and excretion: Ammonia to urea (urea cycle), bilirubin, cholesterol, drug metabolites
  • Storage Function: Vitamins A, D, E, K and B12
  • Production of bile salts: Helps in digestion
• Some examples of liver dysfunction

  • Hepatocellular disease
  • Cholestasis (obstruction of bile flow)
  • Cirrhosis
  • Hepatitis
  • Jaundice
  • Liver cancer
  • Steatosis (fatty liver)
  • Genetic Disorders: Hemochromatosis (iron storage)
• Liver Function Tests (LFTs)


  • Noninvasive methods for screening of liver dysfunction
  • Help in identifying general types of disorder
  • Assess severity and allow prediction of outcome
  • Disease and treatment follow up
• Classification of LFTs


  • Group I: Markers of liver dysfunction: Serum bilirubin, Urine: bile salts and urobilinogen, Total protein, serum albumin and albumin/globulin ratio, Prothrombin Time
  • Group II: Markers of hepatocellular injury: Alanine aminotransferase (ALT), Aspartate aminotransferase (AST)
  • Group III: Markers of cholestasis: Alkaline phosphatase (ALP), g-glutamyltransferase (GGT)
• Limitations of LFTs


  • Normal LFT values do not always indicate absence of liver disease: Liver a has very large reserve capacity
  • Asymptomatic people may have abnormal LFT results: Diagnosis should be based on clinical examination
• Bilirubin


  • A byproduct of red blood cell breakdown
  • It is the yellowish pigment observed in jaundice
  • High bilirubin levels are observed in: Gallstones, acute and chronic hepatitis
• Urobilinogen (UBG) and bile salts

  • Most UBG is metabolized in the large intestine but a fraction is excreted in urine (less than 4 mg/day)
  • Normally bile salts are NOT present in urine
  • Obstruction in the biliary passages causes: Leakage of bile salts into circulation, Excretion in urine
• Serum Albumin


  • The most abundant protein synthesized by the liver
  • Normal serum levels: 3.5 – 5 g/dL
  • Synthesis depends on the extent of functioning liver cell mass
  • Longer half-life: 20 days
  • Its levels decrease in all chronic liver diseases
• Serum Globulin


  • Normal serum levels: 2.5 – 3.5g/dL
  • a and b-globulins mainly synthesized by the liver
  • They constitute immunoglobulins (antibodies)
  • High serum g-globulins are observed in chronic hepatitis and cirrhosis: IgG in autoimmune hepatitis, IgA in alcoholic liver disease
• Albumin to globulin (A/G) ratio

  • Normal A/G ratio: 1.2/1 – 1.5/1
  • Globulin levels increase in hypoalbuminemia as a compensation
• Prothrombin Time (PT)


  • Prothrombin: synthesized by the liver, a marker of liver function
  • Half-life: 6 hrs. (indicates the present function of the liver)
  • PT is prolonged only when liver loses more than 80% of its reserve capacity
  • Vitamin K deficiency also causes prolonged PT
  • Intake of vitamin K does not affect PT in liver disease
• Aspartate aminotransferase (AST)


  • Normal range: 8 – 20 U/L
  • A marker of hepatocellular damage
  • High serum levels are observed in: Chronic hepatitis, cirrhosis and liver cancer
• Alanine aminotransferase (ALT)


  • More liver-specific than AST
  • Normal range (U/L): Male: 13-35, Female: 10-30
  • High serum levels in acute hepatitis (300-1000U/L)
  • Moderate elevation in alcoholic hepatitis (100-300U/L)
  • Minor elevation in cirrhosis, hepatitis C and non-alcoholic steatohepatitis (NASH) (50-100U/L)
  • Appears in plasma many days before clinical signs appear
  • A normal value does not always indicate absence of liver damage
  • Obese but otherwise normal individuals may have elevated ALT levels
• Alkaline phosphatase (ALP)


  • A non-specific marker of liver disease
  • Produced by bone osteoblasts (for bone calcification)
  • Present on hepatocyte membrane
  • Normal range: 40 – 125 U/L
  • Moderate elevation observed in: Infective hepatitis, alcoholic hepatitis and hepatocellular carcinoma
  • High levels are observed in: Extrahepatic obstruction (obstructive jaundice) and intrahepatic cholestasis
  • Very high levels are observed in: Bone diseases
• 1. glutamyltransferase (GGT)


  • Used for glutathione synthesis
  • Normal range: 10 – 30U/L
  • Moderate elevation observed in: Infective hepatitis and prostate cancers
  • GGT is increased in alcoholics despite normal liver function tests: Highly sensitive to detecting alcohol abuse