Bilirubin Direct, Serum

CPT CODE:

USEFUL FOR:

Evaluation of jaundice and liver functions.

SPECIMEN REQUIRED:

Draw blood in a plain, red-top tube(s) or a serum gel tube(s). Spin down and send 0.5 mL of serum refrigerated or frozen inamber vial (# Supply T192) to protect from light.Note:    Patient's age and sex are required on request                   form for processing.

TRANSPORT TEMPERATURE:

Refrig\Frozen OK\Ambient NO

CLINICAL INFORMATION:

Approximately 85% of the total bilirubin produced is derived fromthe heme moiety of hemoglobin while the remaining 15% is producedfrom the red blood cell precursors destroyed in the bone marrowand from the catabolism of other heme-containing proteins. Afterproduction in peripheral tissues, bilirubin is rapidly taken up by hepatocytes where it is conjugated with glucuronic acid to producemono- and diglucuronide, which are excreted in the bile. Directbilirubin is a measurement of conjugated bilirubin.
Jaundice can occur as a result of problems at each step in themetabolic pathway. Disorders may be classified as those due to:increased bilirubin production (e.g. hemolysis and ineffectiveerythropoiesis), decreased bilirubin excretion (e.g. obstruction andhepatitis), and abnormal bilirubin metabolism (e.g. hereditary andneonatal jaundice).
Inherited disorders in which direct bilirubinemia occurs includeDubin-Johson syndrome and Rotor Syndrome. Jaundice of thenewborn where direct bilirubin is elevated includes idiopathicneonatal hepatitis and biliary atresia. The most commonly occurringform of jaundice of the newborn, physiological jaundice, results inunconjugated (indirect) hyperbilirubinemia. Elevated unconjugatedbilirubin in the neonatal period may result in brain damage(kernicterus). Treatment options are phototherapy and, if severe,exchange transfusion.
The increased production of bilirubin that accompanies the prematurebreakdown of erythrocytes and ineffective erythropoiesis results inhyperbilirubinemia in the absence of any liver abnormality. Inhepatobiliary diseases of various causes, bilirubin uptake, storageand excretion are impaired to varying degrees. Thus both conjugatedand unconjugated bilirubin is retained and a wide range of abnormalserum concentrations of each form of bilirubin may be observed. Bothconjugated and unconjugated bilirubin are increased in hepatocellulardiseases, such as hepatitis and space-occupying lesions of the liver; andobstructive lesions such as carcinoma of the head of the pancreas,common bile duct, or ampulla of Vater.

CLINICAL INTERPRETATION:

Direct bilirubin levels must be assessed in conjunction with total andindirect levels and the clinical setting.

REFERENCE VALUES:

0-11 months:  Not established

> or = 1 year:  0.0-0.3 mg/dL