Bromocresol purple and the measurement of albumin. Falsely high plasma albumin concentrations eliminated by increased reagent ionic strength.

This study was undertaken to investigate the extent of the reported discrepancy between serum and plasma albumin concentrations measured by the bromocresol purple (BCP) method. We have shown that plasma albumin concentrations are falsely increased by turbidity due to the precipitation of fibrinogen when plasma is diluted into the BCP reagent. Modification of the BCP buffer (to 0.1M acetate containing 0.15M NaCl, pH 5.5) eliminates the turbidity and thus permits the measurement of albumin in either serum or plasma. Plasma albumin concentrations measured with the modified BCP reagent show excellent correlation with results by an immunoturbidimetric method.