The Use of Platelet Serotonin Release as a Sensitive Method for Detecting Anti‐Platelet Antibodies and a Plasma Anti‐Platelet Factor in Patients with Idiopathic Thrombocytopenic Purpura*

Abstract

Summary. The method described in this paper can be used for detecting anti‐platelet iso‐, hetero‐, and drug‐antibodies and for detecting a factor in the plasma of patients with idiopathic thrombocytopenic purpura that attaches to platelets (ITP factor). Plasma from the test subject, anticoagulated with citrate, is added to a suspension of normal platelets labelled with [14C] serotonin and the amount of radioactivity (serotonin) released is measured after incubating the mixture for 45 min at 37°C. Anti‐platelet antibodies and drug antibodies that fix complement as well as isoantibodies not detectable in vitro by complement fixation or agglutination can be measured by this test. Plasma from 24 of 40 patients with ITP released significantly more serotonin than control plasmas (P < 0.025). False positive results were obtained in less than 2.5% of plasmas from normal individuals, from patients with a variety of diseases and from patients with secondary thrombocytopenia. However, plasmas from two of 13 patients with systemic lupus erythematosus and normal platelet levels gave positive results in the test. The 7S gamma globulin fractions of plasmas containing isoantibodies or ITP factor as well as acid eluates from platelets which had been incubated in these plasmas gave positive serotonin‐release tests.