Heparin-induced thrombotic thrombocytopenia

Heparin-induced thrombocytopenia

There are two types of heparin-induced thrombocytopenia. Type I is more common, has an early onset, and is mild, transient, and benign. Type I is due to direct heparin-induced platelet aggregation and is rarely associated with thromboembolic sequela. Type II is infrequent, has a late onset, and is more severe. Type II is due to an immune-mediated platelet aggregation caused by IgG and IgM that becomes bound to platelets. In Type II, the antibody titers decline over several months; however, early reexposure can result in a catastrophic secondary immune response. Frequently, Type II is associated with life- or limb-threatening thromboembolic complications (white clots), including stroke.

The heparin induced thrombosis--thrombocytopenia syndrome (H.I.T.T.S.): a review

Thrombocytopenia and thrombosis occurring as a direct consequence of heparin therapy are being recognized with increasing frequency in recent years. Current conceptions of the pathophysiology of this syndrome are explained, together with the mechanisms leading to the clinical features. The clinical spectrum of H.I.T.T.S. is widening, but there are diagnostic problems arising from a lack of awareness of the syndrome by some practising clinicians. Many laboratory methods for detecting H.I.T.T.S. have been used, but particular attention should be given to the method of platelet aggregometry. Finally, problems encountered in diagnosis and management of this condition are discussed.

Heparin-induced thrombocytopenia: a prospective study

Thrombocytopenia is a well-described complication of heparin therapy. Few studies describe the incidence of thrombocytopenia when low-dose heparin (10,000-15,000 units/day) is used for prophylaxis of deep venous thrombosis. In our study, ten of 66 courses (15%) of heparin prophylaxis in coronary care unit patients were accompanied by a mild thrombocytopenia with platelet counts below 150 X 10(3)/mm3. In all cases the platelet count returned to normal despite continued heparin therapy. Patients who became thrombocytopenic had significantly lower initial platelet counts. No cases of severe thrombocytopenia were seen (platelet count below 100 X 10(3)/mm3). No patient developed thrombosis, bleeding or elevated fibrin split products. Mild thrombocytopenia occurring after 2-5 days of low-dose heparin is common, but clinically insignificant.

Heparin-induced thrombocytopenia--association with a platelet aggregating factor and cross-sensitivity to bovine and porcine heparin

Heparin-induced thrombocytopenia is an infrequently suspected adverse drug reaction since its sequelae often mimic the underlying condition for which the drug is being used. A concomitant decline in platelet count and increase in heparin requirements should alert the clinician to the possible presence of this disorder. A 36-year-old black male developed severe thrombocytopenia with thrombosis while being treated with porcine intestinal mucosal heparin. Platelet counts returned to near-normal levels upon discontinuation of heparin, but quickly dropped again upon resuming treatment with bovine lung heparin. The patient subsequently was treated with warfarin and dipyridamole, with no further complications. Treatment of delayed-onset severe heparin-induced thrombocytopenia consists of stopping the heparin and substituting antiplatelet agents and oral anticoagulants when continued inhibition of coagulation is required.

Delayed-onset heparin-induced thrombocytopenia. A potentially malignant syndrome

Delayed-onset thrombocytopenia developed in 12 patients while they were receiving either prophylactic or therapeutic heparin. Five of the patients had thrombocytopenia alone, and seven had thromboembolic complications which contributed to the death of one patient. These complications included deep venous thrombosis (four patients), pulmonary embolism (three patients), myocardial infarction (one patient), sagittal sinus thrombosis (one patient), and femoral artery occlusion (one patient). The diagnosis of heparin-induced thrombocytopenia was delayed for between one and 13 days after the initial complicating event. All patients had heparin-dependent platelet-aggregating factor in their plasma. The characteristics of the heparin-dependent platelet-aggregating reaction were the same in all patients, but the nadir of thrombocytopenia was lower in patients with delayed-onset heparin-induced thrombocytopenia and complicating thromboembolism. These findings highlight the necessity for early recognition of this syndrome and for the prompt withdrawal of heparin to prevent considerable patient morbidity.

Heparin necrosis: an anticoagulant-induced cutaneous infarct

A rare complication of subcutaneous heparin therapy is reported in a 75-year-old man. Large erythematous tender plaque developed in the skin overlying the injection sites. In one area of the abdomen, frank necrosis occurred with subsequent eschar formation. Skin testing with five brands of heparin revealed that the patient had a delayed type of hypersensitivity to heparin. In contrast to coumarin necrosis, heparin necrosis is felt to be a thrombotic phenomenon resulting from immunologically induced platelet aggregation in heparin-sensitive patients. Thrombocytopenia is usually present. The diagnosis can be confirmed by platelet aggregometry and calls for immediate cessation of the heparin injections.