Simple spectrophotometric determination of urinary albumin by dye-binding with use of bromphenol blue.

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Abstract
This procedure for routine quantification of albumin in urine is based on the dye-binding properties of albumin with bromphenol blue. The absorbance of 100 microL of urine mixed with 3 mL of color reagent is measured against blank reagent at 610 nm after 30 s. Results vary linearly with albumin concentration up to 6 g/L. The reaction is pH independent in the physiological range. It is not subject to substantial interference by uric acid, creatinine, calcium, sodium chloride, or bilirubin. The presence of globulins produces a small positive error. Within-run precision (CV) was 4.8, 1.5, and 0.9%, and day-to-day precision was 11.2, 2.0, and 1.9%, for samples containing albumin at about 0.1, 1.0, and 6.0 g/L, respectively. Results by a radial-immunodiffusion method (x) correlated well with those by the proposed method (y): r = 0.986; y = 0.98x + 0.096; n = 64. The method can also be used to detect globulins, such as Bence Jones protein, by measuring the ratio of the absorbance at 30 min to that at 30 s.