Reduction of reaction differences between human mercaptalbumin and human nonmercaptalbumin measured by the bromcresol purple method.

Although the bromcresol purple (BCP) method provides high specificity in measurements of serum albumin concentrations, we discovered a reaction difference between the values for human mercaptalbumin (HMA) and human nonmercaptalbumin (HNA) measured by the BCP. We found that the color intensity of HMA with BCP present in the reduced form in the albumin of fresh serum, was lower than for HNA. While maintaining specificity for albumin, we reduced the reaction difference between HMA and HNA, with the addition of sodium dodecylsulfate and 5,5'-dithiobis(2-nitrobenzoic acid) to the BCP reagent. The mean albumin concentration by the BCP procedure for 63 fresh sera and the 63 sera stored for 2 days at room temperature were 35.6 g/L and 38.1 g/L, respectively. Those by the modified BCP procedure were 39.8 g/L and 39.9 g/L, respectively. The difference in measured values between the fresh and stored sera which is believed to be caused by the conversion of HMA to HNA during the storage of sera was not observed in the case of the modified BCP procedure. Our modified BCP method is effective in eliminating uncertainty of the albumin concentration assigned to assay calibrators for the conventional BCP method.