HIV-positive people using heparin for blood clots are more likely than HIV-negative people using the drug to experience a potentially dangerous drop in their platelet counts, according to a report in the November 15 issue of Clinical Infectious Diseases.

George Thompson III, MD, of the department of internal medicine at the University of Texas Health Science Center in San Antonio, and his colleagues studied the medical records of 53 HIV-positive and 106 HIV-negative patients who were treated with heparin to break up blood clots in the heart, lungs or blood vessels. A potential side effect of heparin treatment is thrombocytopenia—a sharp drop in platelets that can lead to internal bleeding and other complications.

In the study, 29 HIV-positive patients developed thrombocytopenia, 13 of them attributed to heparin treatment. Twenty-one HIV-negative patients developed thrombocytopenia and none of them were attributed to heparin treatment. There are two types of heparin treatment, one called unfractionated heparin (UFH) and the other called low molecular weight heparin (LMWH). The majority of patients who developed heparin-induced thrombocytopenia were treated with UFH, and the authors suggest that it may be safer to use LMWH in HIV-positive patients who require heparin treatment.