Thrombocytopenia more common with UFH than LMWH
MedWire News: Although uncommon, thrombocytopenia occurs more frequently with unfractionated heparin (UFH) treatment than with low molecular weight heparin (LMWH), study findings indicate.
Nicolas Falvo (Centre Hospitalier Universitaire de Dijon, France) and colleagues used data from the international prospective Registro Informatizado de la Enfermedad TromboEmbolica venosa (RIETE) to assess the incidence, risk factors, and prognosis of heparin-induced thrombocytopenia (HIT) according to the type of heparin therapy.
Between 2001 and 2009, 24,401 patients in RIETE had confirmed venous thromboembolism treated with UFH (n=22,178), LMWH (n=1250), or both (n=973). In total, 141 of these patients developed thrombocytopenia, defined as a platelet count of 150,000/mm3 or lower, within 6 months of starting therapy.
The researchers report that the incidence of HIT was significantly higher in patients who received UFH than in those treated with LMWH, at 1.36% versus 0.54%.
Further analysis revealed that there was a significant interaction between the type of heparin therapy and gender on the risk for thrombocytopenia. Specifically, women treated with UFH were 4.9 times more likely to develop thrombocytopenia than those who received LMWH, whereas the risk was only 1.6-fold higher with UFH than with LMWH in men.
Falvo and co-authors remark that "the reasons why women receiving UFH treatment may be at a higher risk than men of developing HIT remain unclear." However, "it is well known that women are more prone than men to experience auto-immune diseases."
In both men and women, the UFH-associated excess risk was confined to patients with VTE that was not related to cancer.
After 1 month of treatment, patients with thrombocytopenia were between three and six times more likely to experience complications (recurrence and major bleeding) or death than those without thrombocytopenia, but the type of heparin therapy did not influence their prognosis. Similar results were observed at 6 months.
The researchers note that a lack of data on laboratory tests for HIT antibodies in the RIETE registry meant they were unable to clinically define HIT. Therefore patients with nonimmune-mediated HIT were likely to have been included in the study.
The authors conclude in the Journal of Thrombosis and Haemostasis that although the overall incidence of HIT was low, its gravity justifies routine platelet count monitoring in patients receiving UFH or LMWH treatment.
They add: "The excess risk associated with UFH versus LMWH treatment is especially high in women suggesting that, in the lack of contra-indications, LMWH should be preferred to UFH in this gender."
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By Laura Dean