Micro-ELISA for the quantitation of human urinary and serum retinol-binding protein

A highly sensitive enzyme linked immunoadsorbent assay for determining retinol-binding protein in urine and serum is described. Commercially available reagents are used. The standard curve ranges from 1.2-24 micrograms/l, recovery of retinol-binding protein added to urine was 99-102% (n = 10) and dilution of urine was linear. The within-assay coefficient of variation ranged from 1.2-3.1% and the day-to-day coefficient of variation from 9.2-10.5% depending on concentration. The correlation with urinary retinol-binding protein determined by radioimmunoassay was good (n = 90, r = 0.95). In vitro experiments show that retinol-binding protein is stable in urine with pH 5.2.