The application of polyethylene glycol to radioimmunoassays used in haemostasis.

Use of polyethylene glycol 6000 in the second stages of double antibody radioimmunoassays for fibrinopeptide A, B-thromboglobulin and platelet factor 4 facilitates the more rapid separation of free from bound antigen, and allows precipitating antiserum to be used in greater dilution. At a final PEG 6000 concentration of 5%, separation of free from bound antigen was complete within 1 hour, and antisera could be used in dilutions 3-9 times greater than those recommended by the manufacturers. PEG 6000 had a negligible effect on the affinity of first stage antibodies for their respective antigens. Radioimmunoassays using PEG 6000 were sensitive to protein concentration, failure to adjust standards to similar protein concentrations as those of test samples causing artefactually low results.