Johns Hopkins Medicine
Media Relations and Public Affairs
Media contact: David March
August 12, 2006
NEWS TIP FROM JOHNS HOPKINS MEDICINE
XVI INTERNATIONAL CONFERENCE ON AIDS, AUG. 13-18, TORONTO, CANADA
LESS-EXPENSIVE TESTS TO DETECT PERSISTANT HIV INFECTION AREN’T UP TO THE JOB, HOPKINS SCIENTISTS SAY
At a time when millions of people in rural Africa are gaining access to much-needed antiretroviral therapies to fight HIV, researchers from Johns Hopkins and elsewhere will present results showing that relatively inexpensive methods more widely recommended to monitor disease progression fall short of expectations after treatment starts.
Hopkins researchers evaluated the sensitivity of two popular, relatively inexpensive tests, Dynabeads and Cytospheres. The tests count blood levels of key immune system cells, CD4 T-cells, which fight HIV. Combinations of antiretroviral therapy raise the number of CD4 T-cells while simultaneously lowering the level of viral activity in the blood, or so-called viral load.
Using blood samples from more than 497 HIV-positive men and women being treated with highly active antiretroviral therapy (HAART) at the Infectious Diseases Institute in Kampala, Uganda, the Hopkins team used low-cost tests to measure CD4 T-cells at the start of therapy and at three-month intervals for up to a year and half. The patients also had benefit of the so-called gold-standard test, a more expensive procedure using flow cytometry.
On average, researchers say, single tests using Dynabeads cost $6, and for Cytospheres, $10. The relatively affordable tests can be read in an outpatient setting with the aid of a low-tech, light microscope that costs on average $750. By contrast, a FACSCount flow cytometry machine can cost over $35,000, and the average test price is $25.
Results showed that although Dynabeads and Cytospheres were highly accurate at the onset of therapy (98 percent and 93 percent, respectively) in counting CD4 T-cells after three months of HAART, when CD4 T-cell counts rose above 200 per cubic milliliter of blood, test sensitivity dropped to 31 percent and 55 percent.
Such decreased sensitivity, researchers say, means the tests could underestimate levels of immune cells, making it only possible to detect when the immune system is on the upswing and not when it is faltering.
On further analysis, the scientists found that the cheaper tests underestimated the actual number of failures by 5 percent and 27 percent, respectively. Even flow cytometry was not that effective at correctly monitoring failures, at 17 percent. Catching these cases is important in HAART because the infected person must be quickly switched to a different drug combination before viral resistance builds up.
Infectious disease specialist Lisa Spacek, M.D., Ph.D., who led the study by researchers in the United States, Canada and Uganda, says physicians in Africa need to know the limitations of the cheaper tests as they treat more people with HAART. Current World Health Organization guidelines recommend monitoring of CD4 T-cell counts as a means of tracking patients’ response to HAART. But Spacek cautions that more expensive testing for viral load is the only validated option left for accurately tracking treatment failures.
Comparison of two manual-based bead assays, Dynabeads and Cytospheres, to FACScount at a public, urban clinic in Kampala, Uganda. F. Lutwama, Hasan Shihab, David Serwadda, M. Kamya, H. Mayanja, Thomas Quinn, A. Ronald, and Lisa Spacek
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(Scheduled for presentation at 12:30 p.m. ET, Monday, Aug. 14; poster presentation #MOPE0124, Poster Exhibition Area, Level 800, South Building of Metro Toronto Convention Center.)