EDTA-DEPENDENT PSEUDOTHROMBOCYTOPENIA - A CLINICAL AND EPIDEMIOLOGIC-STUDY OF 112 CASES, WITH 10-YEAR FOLLOW-UP

In the past 10 years, we have observed 112 cases of EDTA-dependent pse udothrombocytopenia (PTCP) due to in vitro platelet clumping at room t emperature, 93 patients had antiplatelet antibodies (48 IgM, 30 IgG, 3 IgA, and 12 had two different isotypes concomitantly), In 20% of pati ents, the presence of IgM antibodies characteristically accompanied pl atelet agglutination also at 37 degrees C, and in citrated blood, The phenomenon was not age or sex related, nor was it associated with any particular pathology or use of specific drugs, and was present in both healthy subjects and patients with various diseases. Flow cytofluorim etric analysis of CD5-positive a cells, which are responsible for auto antibody production, did not demonstrate any changes in the percentage and absolute number of this lymphocyte subset. Average follow-up was 5 years (6 months-10 years); however, previous clinical records disclo sed that PTCP was present for more than 15 years in four cases, and mo re than 20 years in three others, with no clinical manifestation of di sease. This study confirms that EDTA-dependent PTCP is a phenomenon re lated to the presence of natural autoantibodies with antiplatelet acti vity, devoid of pathological significance. Its clinical interest resid es in the need for its prompt and certain recognition in order to avoi d unnecessary examinations and therapeutic interventions. The best and most rapid technique for obtaining accurate platelet counts in PTCP s ubjects is to collect and examine EDTA blood at 37 degrees C; however, clumping will still be present in about 20% of these cases, and even in citrated blood. To obviate this phenomenon, blood should be collect ed in ammonium oxalate, and platelets counted in a Burker chamber. (C) 1995 Wiley-Liss, Inc.