Heparin as a cause of thrombus progression. Heparin-associated thrombocytopenia is an important differential diagnosis in paediatric patients even with normal platelet counts.

A 15-year-old boy developed deep vein thrombosis of the right leg 9 days after appendectomy. In spite of three courses of thrombolysis with streptokinase and effective heparinization the thrombosis progressed with additional occlusion of the left iliac vein. Although platelet counts were constantly normal, heparin-associated thrombocytopenia was suspected as the cause of the new venous occlusions. This diagnosis was confirmed by detecting heparin-associated antibodies with the heparin-induced platelet activation test. Therapy was instituted replacing heparin by the low molecular weight heparinoid Orgaran. Bilateral recanalization occurred within 6 days. Heparin-associated thrombocytopenia must be considered if thrombosis occurs or progresses despite effective heparinization even in the absence of thrombocytopenia.