bilirubin (conjugated/unconjugated) in serum

Reference interval

• Adults: Male & Female:
  • Bu: 0.0 - 1.1 mg/dL
  • Bc: 0.0 - 0.3 mg/dL
• Neonates:
  • Bu: 0.6 - 10.5 mg/dL
  • Bc: 0.0 - 0.6 mg/dL
  • total: < 1.0 mg/dL

Principle

The Kodak Ektachem Clinical Chemistry Slide (BuBc) is a dry multilayered, analytical element coated on a clear polyester support.

A 10 uL drop of sample is deposited on the slide & evenly deposited on the slide & evenly distributed by the spreading layer. Aided by caffeine, sodium benzoate, & surfactant in the spreading layer, Bu dissociated from albumin & migrated with Bc, through the masking layer to the gel registration layer. Proteins (including the albumin-bound Delta Bilirubin & hemoglobin), as well as lipids & lipocromes, are retained in the spreading layer. The masking layer optically blocks potentially interfering compounds trapped in the spreading layer, thereby, preventing them from being measured. In the gel registration layer, Bu & Bc bind to a cationic mordant. Bilirubin mono- & di-glucuronides, when bound to the mordant, have identical spectra & are quantitated together. As Bc in the vicinity of 400 to 420 nm, Bu & Bc have similar molar absorbtivities; at 460 nm, Bu has a higher molar absorbtivity than Bc. Because of these unique spectral characteristics, the reflection densities at two wavelengths (400 & 460 nm) are used to determine the concentrations of Bu & Bc

The following reaction sequences are involved:
Bilirubin complexes ------------> Bilirubin (Bu  + Bc)
Bilirubin + mordant ------------> Bilirubin-mordant complex

Preparation: No special patient preparation is necessary

Clinical significance

• jaundice has been classified as unconjugated & conjugated hyperbilirubinemia (see jaundice)

Increases

• increased plasma-unconjugated bilirubin occurs in
  • hemolytic disorders
  • Gilbert's Syndrome
  • Crigler-Najjar Syndrome
  • neonatal jaundice
  • ineffective erythropoiesis
  • in the presence of drugs competing for glucuronide
• increased plasma conjugated bilirubin occurs with hepatobiliary disorders, including
  • intrahepatic & extrahepatic biliary tree obstruction
  • hepatocellular injury
  • Dubin-Johnson syndrome
  • Rotor syndrome
• in a stress situation, erthropoiesis & unconjugated bilirubin can increase 10-fold
• serum bilirubin will not exceed 4 mg/dL in patients with normal liver function
• hemolysis can lead to very high unconjugated bilirubin in patients with even mild hepatic disease
• neonatal bilirubin, the sum of Bu & Bc, is increased in erythroblastosis fetalis (hemolytic disease of the newborn), which causes jaundice in the first two days of life
• other causes of neonatal jaundice include
  • physiologic jaundice
  • hematoma/hemorrhage
  • hypothyroidism
  • obstructive jaundice

Specimen

Sample preparation: Collect specimen by standard venipuncture technique. Heparin may be used as an anticoagulant for plasma specimens. Sodium citrate, iodoacetate, sodium fluoride/potassium oxalate & EDTA anticoagulants should not be used.

Promptly remove serum or plasma from the clot or cells & analyze as soon as possible to minimize changes. Conversion of Bc to Bu has been observed, presumably due to hydrolysis of the glucuronide moieties. PROTECT SAMPLE FROM EXPOSURE TO LIGHT.

Handle specimens in stoppered containers to avoid contamination and evaporation. Refrigerate at 2-8 C if analysis is not performed within 4 hours after collection. Freeze specimens at -18 degrees C if analysis is delayed beyond 48 hours.

Minimum sample size of 0.5 milliliter: with an optimum size of 1.0 milliliter or larger.

More general terms

• bilirubin in body fluid
• liver (function) tests (LFT, liver panel, hepatic function panel)

More specific terms

• bilirubin conjugated in serum
• bilirubin unconjugated in serum (indirect bilirubin)

Additional terms

• bilirubin (total) in serum/plasma (TBIL)
• bilirubin diglucuronide; conjugated bilirubin; direct bilirubin
• drugs that may affect liver function tests (LFTs)