Protein A as an immunoadsorbent in radioimmunoassay: usefulness in a rapid assay for urinary luteinizing hormone.

A staphylococcal cell wall protein, designated protein A, is known specifically and rapidly to bind to immunoglobulin G. We have utilized this protein as an immunoadsorbent to separate antigen-antibody complexes from free antigen in a rapid 6-hour radioimmunoassay for urinary human luteinizing hormone (hLH). We have further documented the efficacy of this system and the optimal conditions for this assay. The ability of this assay to provide rapid and reliable measurements of hLH in timed urinary specimens provides a useful tool for determination of the preovulatory LH surge and prediction of the time of ovulation in women.