Evaluation of jaundice and liver functions
Photometric, Diazotized Sulfanilic Acid
Direct Bilirubin, Serum
Patient's age and sex are required.
Supplies: Amber Frosted Tube, 5 mL (T915)
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Amber vial
Specimen Volume: 0.5 mL
1. Serum gel tubes should be centrifuged within 2 hours of collection.
2. Red-top tubes should be centrifuged, and the serum aliquoted into an amber vial within 2 hours of collection.
|Specimen Type||Temperature||Time||Special Container|
|Serum||Refrigerated (preferred)||24 hours||LIGHT PROTECTED|
|Frozen||30 days||LIGHT PROTECTED|
|Ambient||6 hours||LIGHT PROTECTED|
Evaluation of jaundice and liver functions
Approximately 85% of the total bilirubin produced is derived from the heme moiety of hemoglobin while the remaining 15% is produced from the RBC precursors destroyed in the bone marrow and from the catabolism of other heme-containing proteins. After production in peripheral tissues, bilirubin is rapidly taken up by hepatocytes where it is conjugated with glucuronic acid to produce mono- and diglucuronide, which are excreted in the bile. Direct bilirubin is a measurement of conjugated bilirubin.
Jaundice can occur as a result of problems at each step in the metabolic pathway. Disorders may be classified as those due to: increased bilirubin production (eg, hemolysis and ineffective erythropoiesis), decreased bilirubin excretion (eg, obstruction and hepatitis), and abnormal bilirubin metabolism (eg, hereditary and neonatal jaundice).
Inherited disorders in which direct bilirubinemia occurs include Dubin-Johnson syndrome and Rotor syndrome. Jaundice of the newborn where direct bilirubin is elevated includes idiopathic neonatal hepatitis and biliary atresia. The most commonly occurring form of jaundice of the newborn, physiological jaundice, results in unconjugated (indirect) hyperbilirubinemia. Elevated unconjugated bilirubin 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 premature breakdown of erythrocytes and ineffective erythropoiesis results in hyperbilirubinemia in the absence of any liver abnormality. In hepatobiliary diseases of various causes, bilirubin uptake, storage, and excretion are impaired to varying degrees. Thus, both conjugated and unconjugated bilirubin is retained and a wide range of abnormal serum concentrations of each form of bilirubin may be observed. Both conjugated and unconjugated bilirubin are increased in hepatocellular diseases such as hepatitis and space-occupying lesions of the liver, and obstructive lesions such as carcinoma of the head of the pancreas, common bile duct, or ampulla of Vater.
> or =12 months: 0.0-0.3 mg/dL
Reference values have not been established for patients who are <12 months of age.
Direct bilirubin levels must be assessed in conjunction with total and indirect levels and the clinical setting.
Specimens should be protected from light and analyzed as soon as possible; grossly hemolyzed specimens should be rejected because hemoglobin inhibits the diazo reaction and falsely low results may be seen.
It is important to remember that in addition to the mono- and diglucuronide fraction, the direct bilirubin assay will also measure the delta bilirubin fraction. Delta bilirubin is a conjugated bilirubin that is covalently bound to albumin. Therefore, the clearance of delta bilirubin from the serum is similar to the clearance of albumin which has a half-life of approximately 21 days.
1. Tietz Textbook of Clinical Chemistry. Edited by CA Burtis, ER Ashwood. Philadelphia, PA, WB Saunders Company, 1994
2. Roche/Hitachi Modular Analytics Reference Guide, Vol 7
Acidified sodium nitrite produces nitrous acid which reacts with sulfanilic acid (in acidic solution) to form a diazonium salt. The diazotized sulfanilic acid then reacts with bilirubin to form isomers of azobilirubin. In the direct bilirubin assay, only conjugated bilirubin is converted by the diazotized sulfanilic acid. The intensity of the color of azobilirubin is measured photometrically at 570 nm and is proportional to the direct (conjugated) bilirubin concentration.(Package insert: Roche Direct Bilirubin reagent; Indianapolis, IN, October 1999)
Monday through Sunday
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.
|Test Id||Test Order Name||Order LOINC Value|
|Result Id||Test Result Name||
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.