Background:  Retrospective cohort studies of HIV-infected patients suggest an incidence of venous thromboembolism (VTE) of 1 to 2%, 10 times that expected in a comparable HIV^– adult population. The reasons for this elevated risk are unclear. We aimed to investigate the prevalence of established risk factors for VTE in this population and explore novel risk factors for VTE.

Methods:  We assessed the incidence of newly diagnosed VTE, based on radiological tests and clinical course consistent with VTE, in patients of the Johns Hopkins HIV Clinical Cohort. Using non-VTE controls matched on enrollment date and follow-up time, a nested case-control study determined risk factors for VTE.

Results:  We identified 160 cases of VTE, 23% of which occurred among inpatients. The incidence of VTE was 5.1 per 100 person-years of follow-up. Cases and controls did not differ by sex, but black patients were overrepresented among cases (odds ratio of 1.85, p = 0.02), and cases were older than controls (mean 39 years vs 37 years, p <0.001). Cases had more advanced HIV disease than did controls, as evidenced by lower CD4 counts (227 vs 362 cells/mm³, p <0.0001), higher HIV RNA titers (116,325 vs 71,262 p = 0.02), and lower hemoglobin levels (10.9 g/dL vs 12.7 g/dL, p <0.0001) preceding the event. Other factors associated with VTE cases include higher white blood cell counts (6567/mm³ vs 4184 /mm³, p <0.0001), and hospitalization within the prior 3 months (67 vs 12%, p <0.0001). HAART, whether non-nucleoside reverse transcriptase inhibitors (NNRTI) or protease inhibitor (PI) -based regimens, was not associated with VTE. In multivariate analyses, higher risk of VTE was associated with any hospitalization in the past 3 months (OR = 12, p <0.0001), diagnosis of lymphoma (OR = 6.7, p = 0.05), central venous catheter use (OR = 4.8, p <0.0001), and a white blood cell count above the median (OR = 2.0, p = 0.009). A CD4 count >500 cells/mm³, independent of these other risks, was protective (OR = 0.30, p = 0.014)

Conclusions:  We found an even higher incidence of VTE among patients with HIV than has been previously reported. Though most events occurred among outpatients, the strongest predictor of VTE was recent hospitalization. Inflammation, as suggested by white blood cell count elevation, was also independently associated with VTE. A high CD4 count was protective.