Non-separation fluoroimmunoassay of human albumin in biological fluids

Determination of albumin levels in biological fluids by a simple, rapid, non-separation fluoroimmunoassay is described. The method ("indirect quenching" fluoroimmunoassay) employs albumin labelled with fluorescein and antibodies against both albumin and fluorescein. Anti-fluorescein serum is added to the conventional immunoassay mixture of sample (or standard), labelled albumin and anti-albumin serum. The fluorescein groups of the free fraction of the labelled albumin become bound by anti-fluorescein antibody and their fluorescence is quenched, whereas the bound fraction is sterically protected from similar quenching. The extent of quenching thus reflects the relative amounts of the free and bound fractions in the unseparated assay mixture. Correlation studies with an automated immunoprecipitation technique show good agreement.