Public Health Service gives go-ahead for wider use of rapid HIV tests
Accuracy on par with EIAs, and returns for test results up sharply
The Public Health Service has revised its HIV testing recommendations, allowing more widespread use of rapid HIV testing in light of new studies showing that the risks of false-positive results are outweighed by the high increase in people who return for their test results.
The recommendations, published in the Morbidity and Mortality Weekly Report, are based on recent studies demonstrating that rapid HIV tests are as accurate as enzyme immunoassays (EIAs) currently used for screening, and on a mathematical model estimating the potential impact of using rapid testing in publicly funded HIV test sites. Based on the findings, the Public Health Service is urging that health care providers should be able to disclose provisional test results in some circumstances, rather than making patients wait two weeks while a confirmatory test is completed.1
The PHS model indicates that in a single year, nearly 700,000 additional people, more than 8,000 of whom would test positive, would learn their true HIV status if rapid tests were available. This is a 29% increase in the number of HIV-positive people and a 50% increase in the number of HIV-negative people who would receive their results as compared to current counseling and testing procedures.
CDC officials warn, however, that the model estimates approximately 8,000 uninfected people would receive initial false-positive results, requiring them to wait a week until a confirmatory test determined they were actually HIV-negative. Although that number is less than 1% of the 2 million people who test each year in public clinics, health officials say it warrants quality counseling to accompany the use of rapid testing.
Who should receive rapid testing and under what circumstances are governed by several factors.
First, the benefit is greatest in test settings that have a high prevalence of HIV and a low percentage of people who return for test results, such as is the case in many STD clinics. The probability of receiving a false-positive test is dependent on the prevalence of HIV in a population. In a clinic with an HIV prevalence of 10%, for example, testing 1,000 people would be expected to yield 100 true positives and four false positives. If the testing took place in a family planning clinic with an HIV prevalence of .4%, however, providers could expect four true positives and four false positives. In that case, only half of the people would be truly positive.
Secondly, people who could benefit greatly from immediate treatment would be good candidates for rapid testing. A pregnant woman about to deliver a child or a health care worker stuck by a needle would benefit from having immediate test results, the CDC notes.
At present, only one rapid test, SUDS HIV-1, an EIA produced by Murex of Norcross, GA, is approved by the FDA, which prohibits the disclosure of provisional rapid-test results. With the new PHS guidelines, the FDA is expected to change that restriction, opening up the market for rapid HIV screening tests. Two new tests are in clinical trials, and a third is already available. (See complete list in AIDS Alert, March 1998, pp. 25-27.)
"Unfortunately, only one rapid test is currently licensed in the United States, and the reasons for that are various but they are not necessarily because they don't perform well," says Stephen McDougal, PhD, chief of the HIV immunology and diagnostic branch in the division of AIDS, STD, and TB laboratory research at the CDC's National Center for Infectious Diseases. As many as 40 manufacturers are working on some type of rapid HIV test, he adds.
The CDC's new position will mean that HIV testing is not limited to the clinic, and that testing can be performed as a street outreach, particularly in high-risk areas. Nonetheless, rapid testing raises ethical and psychological concerns about patients receiving on-the-spot information about a life-threatening disease.
Counseling is critical
Because rapid tests are not 100% accurate, the CDC recommends that quality counseling accompany their use. As with traditional HIV testing, counseling must be tailored to the individual and emphasize the need for confirmatory testing. Counseling should include a discussion of how HIV prevalence influences the degree of test-result certainty, the CDC notes.
Currently, the CDC is revising its guidelines for HIV counseling and testing, which will provide additional recommendations on rapid testing. The agency also is working with communities to help train counselors who use rapid testing and will re-evaluate current testing-and-counseling algorithms when additional rapid tests become available.
"With a focus on quality, client-centered counseling, the disadvantages of rapid testing can be minimized," the CDC states.
1. Centers for Disease Control and Prevention. Update: HIV counseling and testing using rapid tests - United States, 1995. MMWR 1998; 47:211-215.