Monday, November 29, 2004

CATCH: Heparin-Induced Thrombocytopenia (HIT) Much More Frequent than Expected
By Pat French

Heparin is one of the most widely used anticoagulants in the world. In a new DCRI registry, though, people receiving the drug were much more likely to suffer a potentially life-threatening complication than had been thought previously.

Preliminary results of the multicenter Complications After Thrombocytopenia Caused by Heparin (CATCH) registry show that 33% of patients receiving unfractionated (standard) heparin developed thrombocytopenia, or an abnormally low platelet count. Even among patients receiving the drug for less than a week, 20% of them developed this complication, as did 11% to 17% of the patients given a low-molecular-weight (LMW) heparin. These unexpected findings were presented at the 2004 American Heart Association Scientific Sessions.

The DCRI’s Dr. Gustavo Oliveira and colleagues also analyzed prolonged heparin use to determine predictors of low platelet counts, the use of testing for an immune response to heparin, and outcomes among people with low platelet counts.

The strongest independent predictors of thrombocytopenia were lower baseline platelet counts, duration of heparin therapy, admission for cardiac or vascular surgery, acute coronary syndromes, the use of intravenous standard heparin, and a lower body mass index. The group also found that measuring the drop in platelet count from the original count was the most important independent predictor of in-hospital death, followed by older age, number of days on heparin, and occurrence of complications due to blood clots.

Oliveira told theheart.org that fewer than 10% of patients with low platelet counts had undergone testing to see whether an immune response to heparin treatment had caused the thrombocytopenia. Of those who did, 22% had a positive test result. Patients treated with intravenous standard heparin whose platelet count dropped were most likely to undergo such testing.

Patients who developed thrombocytopenia were almost 4 times more likely to die in the hospital than were patients with normal platelet counts. They also were more likely to have heart attack, stroke, congestive heart failure, shock, or major bleeding while in the hospital.

"We need to stop heparin quickly," Oliveira emphasized, noting that, based on the findings of this study and current guidelines, switching heparins (from LMW to unfractionated heparin, for example) is not safe.

"Based on our data, we suggest that a more careful platelet-count monitoring during specific time periods is needed, for example, between day four and 14 after initial heparin exposure," Oliveira told theheart.org.

"We also provide strong evidence that the size of the drop in platelet count (such as a drop of 50% from the original count) is a better measurement for the clinical detection of heparin-induced thrombocytopenia." Oliveira points out that these findings match the recent recommendations from the American College of Chest Physicians.