Enzyme immunoassay: an improved determination of urinary albumin in diabetics with incipient nephropathy

Abstract

An enzyme linked immunoadsorbent assay for urinary albumin using commercially available reagents is described. The assay range is 2.5–120 μg/1. When samples are analysed in two standard dilutions, the assayable albumin concentration range is 2.5–240 mg/1, covering the clinical range from normo-albuminuria to overt clinical nephropathy. Intra-assay variation was 2.1% and interassay variation 8.3%. Recovery of added albumin to urine was 95%–106% and dilution of urine was linear. The correlation to urinary albumin determined by immunodiffusion was excellent (n=80, r=0.99). Intraindividual variation of the 24h urine albumin excretion of different days was high in patients with incipient diabetic nephropathy (51.5%) and was only slightly reduced by taking the variation of creatinine excretion into account (39.5%). No correlation was found between albumin excretion, and HbA_lc or urine glucose excretion, indicating that minor metabolic variations are not responsible for the huge intraindividual day-to-day variations of UalbV. The study shows that more than one UalbV measurement must be done before classifying patients into groups with or without incipient diabetic nephropathy.