Ultrasensitive time-resolved immunofluorometry of human albumin in urine using monoclonal antibodies--a new assay for microalbuminuria.

We describe a two-site, sandwich methodology for human albumin in urine. In the assay, albumin binds to a solid-phase monoclonal antibody and to another monoclonal that is biotinylated. The immunocomplex is then quantified by adding streptavidin which is labelled with an europium chelator, using time-resolved fluorometry. The assay is extremely sensitive (less than 1 microgram/L and specific. A sample predilution of 251-fold or more is needed before analysis. The analytical parameters studied (precision, recovery, linearity, comparisons) were found to be satisfactory. The assay is simple to perform and is proposed as a non-isotopic alternative to radioimmunoassay for the quantification of small amounts of albumin in urine for the purpose of assessing microalbuminuria.