Thromboembolic complications in an asplenic HbE-beta-thalassaemia patient.

A patient, double heterozygous for HbE-beta-thalassaemia, had recurrent thromboembolic complications following splenectomy. In addition to marginally decreased protein C and S plasma levels, laboratory studies revealed a persistent thrombocytosis and markedly elevated plasma concentrations of platelet factor 4 (PF4). PF4 neutralizes the heparin anticoagulant activity. The increased PF4 levels explained the initial heparin resistance observed during anticoagulant treatment in this patient. Subsequent heparin loading tests revealed an abnormal reaction of the PF4 plasma levels, i.e. no increase of PF4. However, upon repeated heparin injections this PF4 response normalized, which may be due to depletion of the endothelial cell associated heparin mobilizable PF4 pool. These observations may be of relevance for the treatment of similar patients.