A new screening method for proteinuria using Erythrosin B and an automated analyzer--rapid, sensitive and inexpensive determination.

In spite of the urgent necessity for a screening test of urinary protein for the early diagnosis of kidney diseases, a rapid, accurate and cost-effective method for their detection has yet to be developed. A solution containing a buffer agent (pH 2.3) and surfactants and a solution of Erythrosin B are added to a urine sample. After letting the mixture stand for 5 min at 37°C, the dye-bound protein is measured by a spectrophotometer at 546 nm using a Hitachi 7170S automated analyzer. The calibration curve was linear with human serum albumin concentration in the range of 2.4-200 mg/l. The detection limit, 2.4 mg/l was superior to conventional dye-binding methods by one order of magnitude and comparable to the turbidimetric immunoassay (TIA). Spot urine samples from 70 patients who showed (-) or (±) in the dip-stick screening test for proteinuria and 79 healthy volunteers were analyzed. There was an excellent correlation (r=0.978, n=149) between the results given by the proposed method and those by the TIA. This method provides a viable alternative to the conventional immunoassay-based methods for urinary protein measurement, and will be useful in the diagnosis of early stage kidney disease.