Serum Bilirubin

Serum Bilirubin

Introduction

      Spectrophotometric determinations of serum bilirubin in clinical laboratory measures two pigment fractions: (1) The water soluble conjugated fraction that gives a direct reaction with diazo reagent and consist largely of conjugated bilirubin. (2) The lipid soluble indirect – reaction fraction that represents primarily unconjugated bilirubin.

Indications

Differential diagnosis of disease of hepatobiliary system and pancreas and other

Causes of jaundice.

 

Normal levels
Total bilirubin	Direct bilirubin
0.1 – 1.2 mg/dL	0.03 – 0.5 mg/dL

 

Increased in

Direct (conjugated) Bilirubin in

20 -40% of total: more suggestive of hepatic than posthepatic jaundice, 40 -60% of total: occur in either hepatic or posthepatic; > 50% of total: more suggestive of posthepatic than hepatic jaundice; total serum bilirubin > 40mg/dl indicates hepatocellular rather than extrahepatic obstruction.

Conditions

·        Hereditary disorders (e.g. Dubin Johnson syndrome, Rotor's syndrome)

·        Biliary duct obstruction (extra and intrahepatic)

·         Hepatic cellular damage (viral, toxic, alcohol/ drug related)

·        Infiltration, space – occupying lesions (e.g. metastatic tumor, abscess, granulomas)

  Increased unconjugated (indirect) bilirubin in

Increased bilirubin production; hemolytic diseases (e.g. hemoglobinopathies, RBC enzyme deficiencies, disseminated intravascular coagulation (DIC), autoimmune hemolysis); ineffective erythropoiesis; blood transfusions; hematomas; hereditary disorders (e.g. Gilbert's disease, Crigler – Najjar syndrome); drugs causing hemolysis.