Findings come from the Women's Interagency HIV Study, or WIHS, a prospective study of women living with HIV (as well as HIV-negative women for comparison) in six urban areas across the United States. In this portion of the study, researchers looked at 1,990 HIV-infected women and 553 HIV-negative women.
When entering the study, 15 percent of HIV-positive women and less than 2 percent of the HIV-negative women had low blood platelet counts, also called thrombocytopenia. Platelets are minute cells in the blood that help in the blood clotting process.
The researchers found that women with thrombocytopenia-a platelet count of fewer than 50,000 platelets per cubic millimeter-had a five-fold increase risk of dying due to any cause, compared to women with normal platelet counts. Thrombocytopenia also was linked to a three-fold risk of dying due to AIDS.
"Only a low CD4+ lymphocyte count, one under 200 cells per cubic millimeter, could compare in the strength of its link to mortality," says WIHS principal investigator Alexandra M. Levine, M.D., Distinguished Professor of Medicine, chief of hematology at the Keck School of Medicine of USC and medical director of the USC/Norris Cancer Hospital. Physicians have long relied on counts of CD4+ lymphocyte as a key measure of immunosuppression in HIV-infected patients.
Fortunately, many women saw their platelet counts boosted back to normal through use of highly active antiretroviral therapy, or HAART, especially therapy containing zidovudine, also called AZT.
Researchers found that factors associated with increased risk of thrombocytopenia included HIV infection, low CD4+ lymphocyte counts, increasing viral load, and smoking. Interestingly, they also found that African-American women appeared to have significantly less risk of thrombocytopenia than white women, a finding that echoes prior research findings.
Researchers are unsure why low platelet counts are associated with decreased survival among HIV-infected women, and more study is needed. Since megakaryocytes- which give rise to platelets-can actually be infected by HIV, it is possible that low platelet counts are simply an independent marker of advanced HIV disease, Levine says.
Calif. Poster session: Disorders of Platelet Number or Function I, Dec. 5, 6 p.m.
The National Institute on Allergy and Infectious Diseases, National Cancer Institute, National Institute of Child Health and Human Development, National Institute of Dental Research and National Institute on Drug Abuse all fund the expansive WIHS project.
Authors for this presentation include researchers from the Keck School of Medicine of USC, Cook County Hospital in Chicago, UC San Francisco, Montefiore Medical Center in New York, Johns Hopkins University, Georgetown University Medical Center, Maimonedes Medical Center (SUNY Downstate) in New York, and the National Institute of Child Health and Human Development.
C. Leigh Pearce, Wendy J. Mack, Alexandra M. Levine, Jay Gravink, Mardge H. Cohen, Edward L. Machtinger, Kathryn Anastos, Michael J. Silverberg, Mary A. Young, Howard Minkoff and D. Heather Watts. "Thrombocytopenia is a Strong Predictor of All-Cause and AIDS-Specific Mortality in Women with HIV: The Women's Interagency HIV Study." 46th Annual Meeting of the American Society of Hematology, San Diego.