Hyperbilirubinemia in Anicteric Blood?

Abstract

CASE DESCRIPTIONPlasma total bilirubin for a 65-year-old man was high [19.1 mg/dL (326 mol/L)] on a Roche cobas 6000 analyzer. However, the specimen was anicteric and the icteric index was 1 (approximately 1 mg/dL or 17 mol/L). A dilution study demonstrated nonlinear results. Direct bilirubin was measured as normal. The split specimen aliquots were further measured on analyzers from 5 different manufacturers (Table 1). The patient's total protein and albumin were 93 and 34 g/L (reference intervals: 60 -80 and 38 -50 g/L). QUESTIONS 1. What might cause artifactual hyperbilirubinemia in anicteric blood? 2. What strategies can be employed to deal with spurious increased bilirubin results?The answers are below. ANSWERSThe patient's serum IgG, IgM, and IgA concentrations were 3.9, 0.1, and 39.2 g/L, respectively. Protein electrophoresis revealed an IgA-paraprotein (38.3 g/L), a small Bence Jones in serum, and a prominent Bence Jones (27.3 g/day) in urine.