Bromcresol purple dye-binding methods underestimate albumin that is carrying covalently bound bilirubin.

We used automated and manual versions of two commonly used dye-binding methods for albumin to quantify albumin that had been modified by covalent addition of bilirubin. Dye-binding methods based on reaction with bromcresol purple underestimated the modified albumin by as much as 29%. Dye-binding methods based on reaction with bromcresol green were unaffected by the presence of covalently attached bilirubin. Neither method was affected by the presence of noncovalently bound bilirubin.