Amid all that conflicting treatment info, there’s one old faithful: Viral load (VL) is the best measure of HIV progression. Or is it? It’s certainly the best gauge of whether your HIV meds are working. But a recent study questions whether VL is good for another use: predicting if and when people who are not yet taking meds will need them.

Since 1996, when John Mellors, MD, found that, on average, people with high viral loads get sicker quicker, doctors have used VL in deciding when to start meds. But a recent study in the Journal of the American Medical Association says viral load may not be the best indicator of when your CD4 count will dive. Tracking 2,800 people with HIV but off treatment, the study “shows that viral load can predict only about 4% to 6% of CD4 [losses],” says study researcher Steven Deeks, MD.

The findings challenge the old analogy of HIV as a train heading for a cliff (AIDS). CD4 count is the distance to the cliff; VL, the train’s speed. Deeks now says those with low VLs may rush cliffward, while others with high VLs may inch along. The difference lies in individual factors. “We need to find out what those are,” he adds.

Others challenge the study. Mellors says, “We’ll publish unequivocal evidence refuting it.” Meanwhile, you and Doc should evaluate all your lab numbers—and your own unique qualities—to decide when to count on a combo.