Variables associated with radioimmunoassay of prostaglandins in plasma

This study examined a number of variables which influence radio-immunoassay measurements of prostaglandins in plasma. Comparative assays in specimens obtained from normal subjects and processed by different methods demonstrated that prostaglandin measurements were uniformly lower when blood was anticoagulated with EDTA, aspirin or indomethacin was added to inhibit further synthesis or prostaglandins in vitro, samples were centrifuged at 4 degrees C at speeds which removed platelets from the sample, and assays were performed when plasma was thawed for the first time. Examination of assay results also revealed that the presence of unextracted plasma enhanced the binding of labeled ligands to antisera (%Bo) but thereafter, the displacement of ligand by increasing quantities of the reference prostaglandin paralleled the results in buffer throughout the range of the assay. In subsequent studies therefore the %Bo for plasma assays was adjusted on the basis of ligand binding in the presence of comparable volumes of pooled plasma from aspirin-treated subjects. Results of 7 prostaglandin assays in plasma and serum of normal subjects are reported.