Viral-load tests tell us the amount of HIV in the blood by measuring RNA, a part of HIV that the virus needs to reproduce. In the U.S., there are two types of viral-load tests, which basically measure the same thing: PCR (quantitative polymerase chain reaction, also called Q-PRCR or RT-PCR), made by Hoffmann-La Roche, and b-DNA (branched chain DNA), made by Chiron Corp. (A third type, NASBA or nucleic acid sequence-based amplification, is used mainly in Europe.)
Several recently published studies -- including some that analyze many years of patients' bloodwork -- have found that viral load is better than CD4 counts at predicting disease progression. As doctors and PWAs have gained more experience in using viral-load tests to predict disease progression and make treatment decisions, some tentative correlations have been developed. The following table is adapted from patient education materials published in the April 1996 issue of AIDS Clinical Care :
|VIRAL LOAD||RISK FOR WORSENING OF DISEASE|
|10,000 or fewer copies per |
cubic millimeter (mm3)
|10,000 to 100,000 copies/mm3||Medium|
|More than 100,000 copies/mm3||High|
This information may change as more experience is accumulated.
Many people have heard about viral-load tests but have had difficulty getting them. Insurance companies and other third-party payers didn't want to pay for them, using the excuse that they were not FDA approved. Furthermore, many doctors were reluctant to use the test, using the excuse that there were no guidelines on how to use them.Finally this is changing.In June, after considerable activist pressure, the FDA approved Hoffmann-La Roche's PCR test, called Amplicor HIV-1 Monitor, for clinical use. Chiron currently is seeking approval of its b-DNA test; approval is expected in early 1997.
Also in June, the IAS-USA panel's recommendations on how doctors should use viral-load tests were published in Nature Medicine. The panel recommends monitoring viral-load levels to determine the risk of disease progression, when patients should start new treatments and when a drug regimen is failing. (However, it is important to remember that other test results, including CD4 counts, and overall health and specific symptoms remain important factors in making treatment decisions.)
To get the most from viral-load tests:
- Use the same test each time (just as you should use the same lab each time you get your CD4s measured).
- Don't get a viral-load test when you have been very sick or within a month of getting a flu shot. These (and other vaccines) can temporarily make your viral load go up.
- Look at overall trends and changes in viral load rather than one test alone.
- Look for large changes. Researchers look for changes of at least 0.5 log (that is, a three-fold change, such as 60,000 dropping to 20,000; a 1.0 log change means a 10-fold change, such as 10,000 increasing to 100,000). Smaller changes are considered unreliable.
|Plasma (blood) HIV RNA level that |
suggests initiation of treatment
|More than 5,000-10,000 copies/mm3 and a CD4 count/clinical status suggestive of progression |
More than 30,000-50,000 regardless of laboratory/clinical status
|Target level of HIV RNA after initiation of treatment||Undetectable*; less than 5,000 copies/mm3 is an acceptable target|
|Minimal decrease in HIV RNA indicative of antiretroviral activity||More than 0.5 log decrease|
|Change in HIV RNA that suggests drug treatment failure||Return toward (or within 0.3 to 0.5 log of) pretreatment value|
|Suggested frequency of HIV RNA measurement||At baseline, take two measurements, two to four weeks apart |
Repeat assessments every three to four months in conjunction with CD4 counting
Measure at shorter intervals as critical decision points are neared
Three to four weeks after initiating/changing therapy
*Undectable means only that the viral load is too low to measure, not that all the virus is gone.
For more information contact: WORLD, Box 11535, Oakland, CA 94611 or 510.658.6930; IAS-USA, 415.675.7430; AIDS Treatment Data Network, 800.734.7104
Chart: International AIDS Society-USA, San Francisco, 1996