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The exact frequency of HIV-associated thrombocytopenia (TCP), defined as platelet count less than 150 x 10(9)/1, was studied in 435 symptom-free HIV-seropositive individuals. At the baseline control, 23 (5.5%) had TCP. TCP individuals had a significantly lower mean CD4 lymphocyte count than the non-TCP individuals. During a mean follow-up of 30 months, 79 out of the 435 individuals (18%) had TCP at least once. During the study period, only 1% of our patients had a platelet count less than 50 x 10(9)/l. TCP was more frequent in intravenous drug users than in other risk groups. A spontaneous normalization of platelet count was observed in more than 50% of TCP individuals.

Important recent advances in the field of the biology of recurrent venous thrombosis include greater understanding of congenital deficiency states involving antithrombin III (AT III) and protein C. Other disturbances demonstrated were related to fibrinolysis frequently, and rarely platelet function and coagulation factors. Possible existence of these anomalies requires investigation during biologic tests in cases of recurrent venous thrombosis, particularly in the presence of a family history or onset of the initial affection before 40 years of age. Confirmation of the importance of screening for such anomalies is supplied by results of a study of 11 families with antithrombin III deficiency and 9 families deficients in protein C, and a literature review of cases. However, currently available biologic tests provide data enabling only partial explanation of the mechanism underlying recurrent venous thrombosis accidents.