TUESDAY, Sept. 26 (HealthDay News) -- A new study questions one of the basic tenets of HIV management -- that the amount of virus in the blood can accurately predict how quickly someone will progress to full-blown AIDS.

Reporting in the Sept. 27 issue of the Journal of the American Medical Association, researchers explain that HIV levels in the blood aren't a good indicator of how fast important immune system cells called CD4 T-cells will decline. A drop in CD4 cells indicates that HIV is progressing to AIDS. HIV levels have also been used as a major factor in deciding when treatment should begin, and this study suggests that viral load levels shouldn't be used as a deciding factor in initiating treatment.

"The dogma has been that if you know how much virus is in the blood, you can know how quickly CD4 levels will go down. If someone had a high viral load, you would assume that person will progress more rapidly to AIDS," said the study's lead author, Dr. Benigno Rodriguez, an infectious disease specialist at Case Medical Center and an assistant professor of medicine at Case Western Reserve University in Cleveland.

And, he said, in large-scale population studies, that assumption is generally correct. But, Rodriguez said, the researchers wanted to know if the same held true on a patient-by-patient basis.

"When we asked that specific question, based on viral load, how much patient-to-patient variability in progression can we explain? The answer was very little -- 6 percent at most," he said.

To explain how doctors used to think of the interplay between HIV levels and the decline of CD4 T-cells, Dr. W. Keith Henry suggested thinking about a train speeding toward a collapsed bridge. He said the distance to the bridge was the number of CD4 T-cells, and that the speed of the train was the level of HIV in the blood.

"In this analogy, the HIV level is the major factor for cell loss in an individual patient," he explained. But, he said, the results of the new study suggest that the HIV levels only account for about 4 percent to 6 percent of the variability of CD4 cell loss in any individual.

"That means there's a lot more going on than meets the eye," said Henry, who added that these findings should spur new areas of research and may lead to better therapies as well as better diagnostics to help with the decision of when to start antiretroviral therapy.

Henry was one of the authors of an accompanying editorial in the same issue of the journal and director of HIV clinical research at the Hennepin County Medical Center and the University of Minnesota.

For the new study, Rodriguez and his colleagues examined two large groups of people infected with HIV -- about 1,500 people in each group -- over a 20-year period. The study participants had not initiated therapy with antiretroviral medications.

The researchers found that "the viral load for the individual has very little predictive value in terms of how rapidly a person is going to progress to AIDS," said Rodriguez.

In fact, he added, "In our study, we had about 10 percent of patients with low viral loads that had extra rapid disease progression, so people should know that having a low load doesn't mean you're OK."

Both Rodriguez and Henry said the measurement of HIV blood levels is still useful as a tool for mentoring the efficacy of antiretroviral therapy.

Since viral load isn't a good gauge for when to begin treatment, Rodriguez said that anyone with a CD4 cell count below 200 definitely needs to start antiretroviral therapy. And those with a CD4 count above 350 can probably wait to start the therapy, which can have side effects. For those with counts between 200 and 350, Rodriguez said the decision of whether or not to start therapy is less clear. He said an analysis of how the immune system is functioning, perhaps by testing the body's response to a vaccination, can help physicians decide if it's time to start treatment.

"One simple number is not sufficient to tell a person where they are in terms of HIV status," Rodriguez said. "There are so many elements involved in the decision to start therapy, and all of these types of judgment calls cannot be made unless you are under the care of an experienced HIV clinician."

More information

For more information about HIV, go to the National Institute of Allergy and Infectious Diseases.