The more expensive method called viral load testing may not provide a substantial benefit over the cheaper and older one, known as cluster of differentiation 4+ (CD4+) testing for monitoring patients with HIV and Acquired Immunodeficiency Syndrome (AIDS).

Scientists at the University of California, San Francisco (UCSF; USA) with others in Canada and Uganda compared the two most common tests for HIV/AIDS disease progression head-to-head and alongside a third strategy, which relied on close clinical monitoring alone, with no testing. Both tests rely on taking routine blood samples from patients and then analyzing the blood for markers of the virus or of immune system functioning. The cheaper test looks at the abundance in the blood of human immune cells, the CD4+ cells. The more expensive test samples the blood for viral load, or copies of viral genomes.

Measuring CD4+ cells in the bloodstream provides a view of HIV disease status. The CD4+ test directly measures the abundance of the helper T-cell, an immune cell in the bloodstream distinguishable because they are the only ones that carry the CD4 marker. Viral load measures the amount of virus a person has in his/her bloodstream. It is closely connected with the state of infection, and in general, as people become very sick with HIV/AIDS, their viral load increases. When people with AIDS are given antiretroviral drugs for the first time, their viral load often drops dramatically as their health improves.

The study was based on the health outcomes of 1,045 people receiving high quality AIDS care in eastern Uganda. Patients in the trial were routinely visited and tested several times a year over the course of the trial. The analysis also showed that viral load testing provided little or no clinical benefit over monitoring CD4+ counts alone, and CD4+ counts proved to provide a substantial benefit at a modest cost. The report also calculated the health benefit of investing in expanded antiretroviral therapy instead of viral load testing. With USD 100 million to spend on HIV, putting the money into antiretroviral therapy with CD4+ testing rather than viral load testing would add 36,000 healthy life years. James G. Kahn, MD, MPH, a professor at UCSF, said, "Viral load monitoring is extremely expensive, if you want to spend money well, you appear better off spending it on antiretroviral drugs." The study was published in December 2, 2011, issue in the British Medical Journal.

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