Two tests work better than one at tracking HIV disease
Two tests work better than one at tracking HIV disease
Use viral load together with CD4 counts
While viral-load testing has gained stature in recent years as the single most important predictor of a patient’s risk of disease progression, two of the most definitive studies on prognostic markers for HIV disease conclude that combining viral-load testing with CD4 counts is more accurate than either of the two measurements alone.
"These studies underscore the value of routinely using both viral-load measurements and CD4 T-cell counts in the care and management of individuals with HIV/AIDS," says Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, which sponsored the studies.
Published in the June issue of the Annals of Internal Medicine, the studies extend the findings of NIAID’s Multicenter AIDS Cohort Study (MACS), which reported last year that viral load was the best way to predict the risk of developing AIDS or dying.1
The researchers measured HIV viral load in baseline blood samples obtained from more than 1,600 HIV-infected men in the MACS study between 1984 and 1985. They discovered that in patients with similar viral loads, CD4 counts were a good predictor of AIDS progression. For example, only 3.5% of patients with 500 or fewer copies of HIV RNA and more than 750 CD4 cells progressed to AIDS within nine years. On the other hand, 22% of patients with the same viral load but fewer than 750 CD4 cells progressed to AIDS during the same period. For sicker patients, nearly 98% who had a viral load greater than 30,000 copies and less than 200 CD4 cells progressed to AIDS within six years.
"These markers were highly predictive of outcome independent of subsequent treatment with nucleoside monotherapy," says lead author John Mellors, MD, professor of medicine at the University of Pittsburgh.
The study reinforced a prevailing notion that patients with high viral loads and low CD4 counts were more likely to develop AIDS than patients with high viral loads and relatively higher CD4 counts.
In a second study published in the journal, researchers from NIAID’s AIDS Clinical Trials Group (ACTG) found that the best way to optimize the prediction of disease progression is to measure viral load and CD4 cells before initiation of treatment, followed by a second viral-load test within three to four weeks after start-up. Indeed, measuring viral load eight weeks after treatment provided yet more prognostic information, the authors note. For every 10-fold decrease in viral load at this point, the risk of disease progression was reduced 52%.
In an editorial accompanying the articles, Michael Saag, MD, professor of medicine at the University of Alabama in Birmingham, underscored three guidelines for routine use of viral-load testing.2 First, clinical decisions should be based on more than one test result, because there can be wide variation among different assays. Also, certain illnesses and vaccinations can alter the levels of viral load.
Second, HIV responds immediately to changes in therapy, and a patient who misses doses before being tested may show a sharp increase in viral load, falsely indicating that the current regimen is failing. Consequently, clinicians should review a patient’s compliance with a regimen and postpone a test if doses have been missed, Saag says.
Third, enough time should elapse before testing to see whether a regimen is failing. Saag points out that there are two phases in the profile of a patient whose viral loads reach undetectable levels. In the first two weeks, the virus rapidly decreases around 100-fold. In the second, slower phase, the rate of decrease levels off, and another 12 to 16 weeks are required for virus to reach undetectable levels.
References
1. Mellors J, Munoz A, Giorgio J, et al. Plasma viral load and CD4 lymphocytes as prognostic markers of HIV infection. Ann Intern Med 1997; 126:946-954.
2. Saag M. Use of HIV viral load in clinical practice: Back to the future. Ann Intern Med 1997; 126:983-984.
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