Timothy R. Sterling, MD, a study co-author and assistant professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health said, "The test could be used to determine when to initiate antiretroviral therapy in HIV-infected persons. And because it costs much less than both CD4 lymphocyte count and HIV-1 RNA viral load, the heat-denatured p24 antigen test could be of particular benefit in developing countries, where the burden of HIV infection is great."
According to Dr. Sterling, CD4 lymphocytes and HIV-1 RNA are excellent predictors of disease progression and response to therapy and are used to determine when to initiate antiretroviral therapy. However, the current tests to monitor CD4 lymphocytes and HIV-1 RNA are expensive. The heat-denatured assay separates antigen-antibody complexes and increases the detection of p24 antigen in patients during the early-stages of the disease.
"P24 antigen is a protein in HIV. The test is administered by drawing blood from a patient, heating the plasma, and then measuring the amount of p24 antigen found in the sample. Higher levels of p24 indicates a greater risk of disease progression," explained Dr. Sterling. The authors found that a p24 level of 5 pg/ml was comparable to a CD4 lymphocyte count of 350 cells/mm3 or a viral load of 30,000 copies/ml (b-DNA).
The 494 participants in the study were injection drug users enrolled in a longitudinal cohort study. Blood samples were obtained and analyzed to quantify T-cell subsets; HIV-1 RNA and p24 antigen were quantified in specimens that had been frozen after collection. Semiannual follow-up interviews were also held with participants during the 5-year study.
Using Johns Hopkins Hospital prices, researchers found that conducting a CD4 lymphocyte count is $88; a HIV-1 RNA level is $152. The total cost of a p24 antigen test is approximately $20 when used qualitatively and $30 when used quantitatively. Because of the frequency with which monitoring must be performed to assess disease progression and response to therapy, researchers said they believe the heat-denatured p24 antigen test would be much more affordable than the currently available tests. In addition, they said the p24 antigen assay is readily automated, easy to perform, and storage is less demanding than that required for other tests.
Sterling said, "The heat-denatured p24 antigen test was comparable with that of the HIV-1 RNA and CD4 lymphocytes. In addition to its low cost, it could be used either alone, or in conjunction with the other tests. It would be very useful in making decisions regarding the initiation of antiretroviral therapy, particularly in resource-poor settings."
Co-Authors of the study were Donald R. Hoover, Jacquie Astemborski, David Vlahov, John G. Bartlett, and Jorg Schupbach.
The study was funded by the Swiss Federal Office of Public Health, Swiss Human Immunodeficiency Virus Cohort Study/Swiss National Science Foundation, National Institute on Drug Abuse, and National Institute of Allergy and Infectious Diseases.
Link to the Johns Hopkins Bloomberg School of Public Health at www.jhsph.edu.