Elevation of platelet factor four in acute myocardial infarction: measurement by radioimmunoassay

A radioimmunoassay has been developed for the measurement of PF-4--a chemically well-defined heparin-neutralizing molecule. PF-4 was iodinated, repurified by affinity chromatography on heparin-Sepharose, and incubated with rabbit antiserum and a source of unlabeled antigen. Following incubation at 4 degrees C for 24 hr, bound PF-4 was precipitated with 2.2M ammonium sulfate. The assay, which could detect 25 pg of purified PF-4, was unaffected by the presence of plasma containing up to 50 U/ml heparin. The plasma concentration of PF-4 in 30 normal subjects was 16 +/- 4 ng/ml. This level was increased in patients with pulmonary emboli, prosthetic cardiac valves, and severe cardiorespiratory failure. In addition, 21 of 50 patients admitted to the hospital with acute chest pain who had sustained a myocardial infarct had a mean level of 95 ng/ml. In contrast, the mean level in 21 patients with chest pain but without evidence of infarction was 29 ng/ml. PF-4 remained elevated for at least 1 week after infarction in six of the eight patients studied and then returned to within the normal range. The data suggest that radioimmunoassay of PF-4 may be a useful test to measure activation of the coagulation system and an aid to the diagnosis and treatment of patients with thromboembolic disorders.