Heparin-induced
thrombocytopenia(HIT) due to immunological mechanisms is known as an important adverse reaction to
heparin treatment, and
heparin treatment should be applied while keeping in mind the risk of onset of HIT 5-14 days after the initiation of
heparin. The presence of HIT had not been fully recognized in clinical practice in Japan despite the management of HIT being well confirmed in Western countries. Recognition of HIT has increased since
argatroban, a
direct thrombin inhibitor, obtained the approval of the FDA for prevention and treatment of HIT. Although the incidence of HIT in Japan has not yet been clarified, there is some evidence that HIT is encountered in
critically ill patients undergoing
heparin anticoagulation. Clinical diagnosis of HIT is performed by means of
thrombocytopenia of a drop of 50% or 100 x 10(30/microl for 5 -14 days after starting
heparin treatment. Confirmatory laboratory tests examine whether the patients have
antibodies against
heparin/PF4 complexes or not. Two assay tests for detecting
heparin/PF4 complex
antibodies are available in Japan. As a functional test, the
heparin-induced platelet aggregation method is easily performed and the result is obtained in a short time. The result of the test has, however, been misleading due to the selection of donors. Low platelet activity of the donors on the addition of
heparin induces a negative response in spite of positive
antibodies in the sample. Before testing samples, it is important to check
heparin reactivity of the donor's platelets.
Enzyme immunoassay detecting the
antibodies is available as a commercial kit. Sensitivity obtained by
enzyme immunoassay is very high and often introduces false-positives. Careful attention to interpretation of the result is required. Treatment of HIT should be started at the time of recognition of
thrombocytopenia while antibody testing for HIT is performed. As an alternative
anticoagulant to
heparin,
argatroban should immediately be applied to avoid complication of
thrombosis.
Thrombocytopenia and
hypercoagulability quickly recover to the preheparin level by the appropriate use of
argatroban.