Development of the fluorometric ELISA method for determination of alpha(1)-microglobulinuria in a cadmium-polluted area in Japan

Objectives: To evaluate the usefulness of a newly developed fluorometric en zyme-linked immunosorbent assay (fluorometric ELISA) method for quantificat ion of alpha1-microglobulin (alpha1-m, protein HC) in an epidemiological st udy. Methods: Urinary alpha1-in in 37 female inhabitants in a cadmium-pollu ted area, including seven cases with Itai-itai disease, and ten inhabitants in a non-polluted area in Japan were examined. The alpha1-m was measured b y both the fluorometric ELISA and a commercially available enzyme immunoass ay (EIA) method to evaluate correlation of the two measurements. Concentrat ion of beta2-microglobulin (beta2-m) was also determined in the same sample s. Results: The detection limit of this method was 3 ng/ml or less of alpha 1-in. A significant, high positive correlation was obtained between the alp ha1-m concentrations measured with the fluorometric ELISA and that of EIA ( r = 0.95, P < 0.0001). A significant association was also shown between the alpha1-in and beta2-m concentrations in the urine samples. The concentrati ons of urinary al-in of the inhabitants in the cadmium-polluted area (mean: 6.21 mg/l, 95% confidence interval (95% CI): 4.06-9.50 mg/1) were signific antly higher than those of the reference area (mean: 2.19 mg/l, 95% CI: 1.9 0-2.67 mg/1). The urinary alpha1-m level of the Itai-itai patients was show n to be highest at 39.63 mg/l (95% CI: 28.27-55.55 mg/1). When the cut-off value of 10 mg/l was employed, alpha1-m had a sensitivity of 100% and speci ficity of 100% for Itai-itai disease. Conclusion: These results suggest tha t this fluorometric ELISA is a useful tool to determine urinary alpha1-m in the epidemiological survey of renal tubular dysfunction, especially in the cadmium-polluted area of Japan.