ELEVATION OF PLATELET FACTOR 4 IN ACUTE MYOCARDIAL-INFARCTION - MEASUREMENT BY RADIOIMMUNOASSAY

Abstract

A radioimmunoassay was developed for the measurement of [platelet factor IV] 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.degree. C for 24 h, bound PF-4 was precipitated with 2.2 M 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. Of 50 patients admitted to the hospital with acute chest pain who had sustained a myocardial infarct, 21 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 wk after infarction in 6 of the 8 patients studied and then returned to within the normal range. 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.