RESUMO
BACKGROUND: A simple spot test was developed, which allows quantification of microalbuminuria. Evaluation was carried out according to the ISO 15189 guidelines. METHODS: Urine was spotted on cellulose acetate strips and stained using different sensitive protein binding dyes (nigrosin, Coomassie Blue R-250, amido black). The colour intensity of the stained spots was quantified using a Kodak Image 450 station. RESULTS: Analytical sensitivity of the Coomassie Blue based method (18 mg/L) was better than that for nigrosin (50 mg/ L) or amido black (100 mg/L) based methods. Within-run coefficient of variation (CV) and between-run CV of the Coomassie blue assay were, respectively, 8.4% and 9.7% (50 mg/L), and 3% and 4.5% (400 mg/L). For nigrosin, these data were, respectively, 8.4 and 9.4 (50 mg/L), and 3.4 and 6.4% (400 mg/L). Coomassie Blue showed a preferential binding selectivity towards albumin. The method was found to be linear between 20 and 600 mg/L. A good correlation (r2 = 0.89) was obtained between Coomassie Blue based and immunonephelometric measurements. Immuno-unreactive albumin (prepared by protease treatment) could be detected by the spot test, which offers an advantage of the method versus immunochemical tests. Ammonium sulphate precipitation could further increase the specificity of the assay by eliminating effects of free light chains. CONCLUSION: The described method is very simple and extremely cheap, which makes it potentially suited for screening programmes, particularly in third world countries.