Serum globulins contribute to the discrepancies observed between the bromocresol green and bromocresol purple assays of serum albumin concentration

The bromocresol green (BCG) and bromocresol purple (BCP) assays often yield discordant serum albumin results. This study seeks to test the hypothesis that bias in albumin results are influenced by the concentration of serum globulin subtypes. The concentrations of serum albumin, alpha 1-globulin, alpha 2-globulin, beta-globulin and gamma-globulin are determined in 197 human serum specimens by total serum protein quantification and protein electrophoresis, and by the BCG and BCP assays. The influence of globulins on albumin measurement is validated with protein mixtures of albumin and globulins. The BCG assay bias was directly proportional to the concentrations of alpha 1-globulin and alpha 2-globulin, and inversely correlated with the concentrations of beta-globulin and gamma-globulin (r(2)=0.793). The BCP assay bias was inversely proportional to the concentration of alpha 1-globulin and alpha 2-globulin (r(2)=0.464) but not related to the concentrations of beta-globulin or gamma-globulin. Among the 197 study participants, those with nephrotic syndrome had a significantly higher level of alpha 2-globulin compared to those in other categories. Thus, the authors conclude that serum globulins contribute to the bias seen in the BCG and BCP assays, with the greatest effects observed for alpha-globulin on the BCG assay where higher concentrations contributed to a higher bias.