New AIDS Tests May Predict Disease’s Course
Two new studies presented here this week indicate that measuring the concentration of HIV in blood predicts the course of AIDS in a patient better than the white-blood-cell counts that have been the mainstay of AIDS diagnosis for 15 years.
A high concentration of HIV--the virus that causes AIDS--suggests a rapid progression to full-blown disease and an early death, according to the findings reported at the 11th International AIDS Conference. A low “viral burden” suggests slow progression and prolonged survival.
For the record:
12:00 a.m. July 12, 1996 For the Record
Los Angeles Times Friday July 12, 1996 Home Edition Part A Page 3 Metro Desk 2 inches; 45 words Type of Material: Correction
AIDS tests--A story in Thursday’s Times erred in reporting that Medi-Cal does not pay for two new kinds of HIV tests. A spokesman for the California Department of Health Services says Medi-Cal pays for one of the tests, known as PCR, and has no policy on the other, which is known as bDNA and is not yet approved for marketing.
Other new evidence shows that such testing also represents the most valuable tool researchers have for monitoring the effectiveness of the highly touted combination-drug therapies and for determining which drugs are most appropriate for which patients.
The tests “may be the most important diagnostic advance for AIDS researchers and clinicians since the development of the test to measure HIV antibodies,” said Dr. Thomas O’Brien of the National Cancer Institute.
“These studies have made it increasingly clear that the CD4 [white-cell] count is at best a gross measure of where a patient stands in the course of HIV disease,” added Dr. Scott M. Hammer of the Harvard Medical School.
But the majority of patients do not have access to the sophisticated tests because they cost up to $200 each and Medicaid, state agencies and most private insurers will not reimburse laboratories that perform them. Until recently, the tests have also been considered experimental.
Access to them “is just as important as access to all the new drugs,” said Dr. Gabriel Torres of St. Vincent Medical Center in New York City. “Unfortunately, nobody will pay for them.”
Dr. John W. Mellors of the University of Pittsburgh Medical Center reported Wednesday on the results of following 1,604 HIV-positive men for 10 years in a massive project called the Multi-Center AIDS Cohort Study. Although the viral load tests are new, researchers had stored blood samples from the men since the beginning of the study and were able to go back and determine how much virus was present earlier.
Mellors told the audience here that viral load measurements are more accurate than CD4 counts, but also that the two taken together provide the most accurate projections for future survival.
The Pittsburgh team found, for example, that men who had the lowest viral loads, less than 500 viruses per milliliter of blood, and the highest white-cell counts, more than 750 per milliliter, when they entered the study had the lowest likelihood of progressing to AIDS in six years, about 1.7%. Those with the highest viral burdens and the lowest white-cell counts had the highest probability, 85.5%.
After nine years, only 3.6% of those in the first group had AIDS, but all of those in the second group did.
Those were the extremes. The team was able to divide the participants into about 10 groups with progressively higher probabilities of having AIDS within a given time.
“By closely monitoring viral activity and immune response, we can now make a more educated assessment of a patient’s disease course, as well as a more informed opinion of how that patient is responding to therapy,” Mellors said.
If an infected person is in the lowest-probability category for progressing to AIDS, Mellors said, he or she may be given no drugs; this averts the disabling side effects that some of the medicines have.
At the other extreme, it is crucial to attack the problem immediately and aggressively with a combination of drugs. The tests make it possible to tailor treatment to each patient, Mellors added. Such information has never been available before.
Similar results were obtained in a study of 391 patients reported Monday by Dr. David Katzenstein of the Stanford University Medical Center. “Measurements of viral burden can help us a lot” in handling patients, Katzenstein said.
The new tests are different from those used to detect whether a person has HIV, or the human immunodeficiency virus, in the blood. That test looks for antibodies that the body produces against the virus, but it reveals nothing about the extent of the infection or how fast the virus is reproducing. About 40 million to 50 million of these tests--which cost only a few dollars apiece--are used every year in the United States.
The two new types of testing determine how much of the virus’ genetic material is present in the blood, and thus how many viruses are present and how fast they are replicating.
One, called PCR, was developed by Roche Diagnostic Systems of Branchburg, N.J., and the other, known as “branched DNA” or “bDNA,” was developed by Chiron Diagnostics of Emeryville. Mellors used the Chiron test; Katzenstein used Roche’s.
Roche’s test was approved for marketing by the U.S. Food and Drug Administration last month, and Chiron’s is expected to be approved soon.
Experts say it is too early to tell whether the Roche or the Chiron test is better, or which will dominate what is expected to become a $500-million-a-year market.
Whether that market develops may depend on whether insurers will pay for them. In late June, the White House sent a strongly worded letter to public insurers in each state recommending that such tests be covered, but most agencies--including Medi-Cal in California--have not changed their policies.
