Oxidation markedly reduces bilirubin interference in the Jaffé creatinine assay

Bilirubin causes underestimation of serum creatinine in the Jaffé alkaline picrate assay. We report an approach for preventing bilirubin interference by pretreating serum samples with peroxidase and H2O2. The dissociation of bilirubin from albumin and its subsequent oxidation markedly reduces the bilirubin interference and enables accurate determination of creatinine concentrations by the Jaffé reaction even in hyperbilirubinemic sera. Within-run CVs were 2.6%, 4.0%, and 3.8% at mean creatinine concentrations of 88, 165, and 349 mumol/L, respectively (n = 20). Day-to-day CVs were 4.0%, 6.3%, and 5.8% for mean creatinine concentrations of 87, 168, and 364 mumol/L, respectively (n = 12). Average recovery of creatinine added to serum in the presence of 600 mumol/L bilirubin was 97% (n = 15). This method requires only small serum volumes (70 microL) and is easily applicable to automated analyzers that can be programmed to add three reagents consecutively.