Clinical observations in thrombocytopenia:

We investigated clinical and laboratory aspects in three different situations of thrombocytopenia in which an immune mechanism is active, i.e. thrombocytopenia caused by autoantibodies (thrombocytopenia induced by the anticoagulant drug heparin (HITT) and immune thrombocytopenic purpura (ITP), thrombocytopenia and platelet alloimmunization and a platelet consumption type of thrombocytopenia (thrombotic thrombocytopenic purpura (TTP). First, we prospectively studied the incidence of HITT using new, will- defined criteria of a proportional fall in the platelet count in combination with the presence of HITT antibodies, in 358 patients with cardiac or neurological complaints. The observed incidence was 0.3%. Secondly, in an evaluation of the predictive value of HLA-antibody testing for the outcome of the first HLA-matched platelet transfusion in thrombocytopenic patients who were refractory to random donor platelet transfusions and who always had received non-leukodepleted blood products in case of transfusion, we found that almost 90% of the patients with a positive HLA test can be treated with HLA matched platelets. Third, in studying ITP patients we found a strong indication that intensive immunosuppressive treatment cannot prevent but only postpone splenectomy as the standard second-line therapy. In addition, the study of serum thrombopoietin levels and platelet kinetics, pointed to an impaired regulation of thrombo- and megakaryopoiesis in ITP. Finally, it was found that splenectomy could be effective in inducing durable remissions and in the prevention of relapse in patients with TTP.