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News 16/10/2544

Heparin-induced thrombocytopenia is well known to occur 5 to 8 days after heparin therapy is started.

Delayed-Onset Thrombocytopenia Described With Heparin Use

WESTPORT, CT (Reuters Health) Oct 08 - Heparin-induced thrombocytopenia is well known to occur 5 to 8 days after heparin therapy is started. However, a delayed form of the disease can occur up to 3 weeks after heparin therapy is stopped, according to a report by Canadian researchers.

In the October 2nd issue of the Annals of Internal Medicine, Dr. Theodore E. Warkentin from Hamilton General Hospital and Dr. John G. Kelton from McMaster University, both in Hamilton, Ontario, describe 12 patients who developed what they term delayed-onset heparin-induced thrombocytopenia.

On average, the patients presented with thrombocytopenia and associated thrombosis 9.2 days after heparin therapy was discontinued (range 5 to 19 days). All developed at least one thrombotic complication. Nine of the 12 patients received additional heparin therapy, which only worsened the thrombocytopenia, and one of these patients experienced cardiac arrest.

The researchers compared serum samples from the subjects with stored samples from patients who had developed non-delayed heparin-induced thrombocytopenia. Samples from patients with delayed-onset disease had higher titers of IgG antibodies to platelet factor 4-heparin and greater IgG-induced heparin-dependent and heparin-independent platelet activation.

It is generally believed that heparin-induced thrombocytopenia can be avoided by limiting the duration of heparin therapy to no longer than 4 days, the investigators point out. However, most of the patients in the current study received heparin for 3 days or less. Use of low-molecular-weight heparin did seem to reduce the risk.

"Physicians should consider delayed-onset heparin-induced thrombocytopenia when a patient presents with thrombosis and unexplained thrombocytopenia up to 3 weeks after the end of heparin therapy," the authors advise. If the complication is not recognized, they note, physicians may fail to use a nonheparin anticoagulant and instead restart heparin, which could lead to a worsening of the patient's condition.

Ann Intern Med 2001;135:502-506.

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