Standardization in Bilirubin Assays: Evaluation of Selected Methods and Stability of Bilirubin Solutions

Abstract

Because of the inaccuracy of bilirubin (BIL) determinations, we have investigated some sources of error associated with the most commonly used methods. Inadequate standardization appears to be the most common error. BIL standards in either human serum albumin (HSA), bovine serum albumin (BSA), or pooled human serum were analyzed by these methods. Molar absorptivities (ε) of azobilirubin by the Jendrassik—Gróf procedure were practically identical in all three protein bases. The Meites—Hogg and Malloy—Evelyn methods gave substantially higher ε values with BIL in serum than with BIL in either HSA or BSA. The precision of all methods was good, but best with the Jendrassik—Gróf procedure. BIL standards can be prepared with good reproducibility (CV <0.5%). Standards deteriorate appreciably at -23 °C but are stable at -70 °C. Our data indicate a need for improved commercial BIL controls.