A Reference for Determination of Bilirubin Concentration in Serum Using Bilirubin in Cyanide-Formamide for Enrichment of Serum

Abstract

Unconjugated bilirubin is highly soluble in formamide with cyanide (0.10 mol/1), giving a solution stable at 25 °C in the dark for 4 hours. Human serum (at pH = 9.5) can be enriched with this solution to at least 430 μmol/1 (250 mg/1) even when the volume fraction of formamide is below 0.02. The bilirubin complex in the ensuing preparation (employing infant serum) seems to have the same stability and spectrophotometric properties as in serum from hyperbilirubinaemic infants. This reference preparation is suitable for standardization of methods using azobilirubin or direct spectro-photometry for the determination of total bilirubin in human serum.

Key Words:

• Azobilirubin
• bilirubin
• cyanide
• formamide
• hyperbilirubinaemia
• reference preparation
• gel chromatography
• spectrophotometry
• standardi zation