Rapid tests could 'revolutionize' screening
Testing services can expect numerous changes
With one rapid HIV test already approved in the United States and several more in the pipeline, health officials are anticipating wide spread change in the way patients are tested and counseled in public health departments. But while the Centers for Disease Control and Prevention is revising its guidelines for counseling and testing, traditional client-centered prevention counseling remains appropriate for rapid HIV testing, at least during the interim.
"Rapid HIV testing will certainly revolutionize how things are done in many places and give us a wider variety of options both for screening and confirmation," says Rick Steketee, MD, chief of the CDC's prevention services research branch in the Division of HIV/AIDS Prevention.
The CDC recently adopted the use of rapid HIV testing for clinics with a high prevalence of HIV and a low number of patients who return for their test results. (See AIDS Alert, March 1998, pp. 25-27.) The only approved rapid test, the Single Use Diagnostic System for HIV-1 (SUDS), by Murex Corp. of Norcross, GA, has a sensitivity (99.6%) that warrants use in high prevalence areas, but in low prevalence settings it would generate too many false-positive tests, CDC officials caution.
The agency's imprimatur for rapid testing is designed to spur development of a new generation of rapid tests that eventually can lead to less restrictive uses, Steketee says. Currently, those clients who receive SUDS and test positive will need a confirmatory test. Several tests are in development that could prove more sensitive and specific than the SUDS, Steketee adds.
Indeed, the CDC has laid the groundwork for a trial that would evaluate the use of two rapid HIV tests as confirmatory tests that could be provided on the same day of the test. With only one approved test on the market, the CDC trial must await the approval of more tests because it would want to evaluate only those tests that will be used in the public domain, Steketee notes.
Once rapid HIV testing becomes more widespread, program and clinic managers will face a host of issues that will alter the landscape of HIV testing and counseling, say CDC officials. Anticipating the need for added information before the new counseling and testing guidelines come out, the agency has released several issue papers for counselors, laboratorians, and patients. (See Common Sense About AIDS insert for basic information about the tests.)
Who should use rapid test
The most immediate question facing clinics is whether HIV rapid testing is appropriate at this time. The CDC avoided defining what it considers high HIV prevalence or low test-return rates because it did not want to dictate too strictly the settings in which rapid testing is appropriate, Steketee says.
"We didn't state it that way," he explains. "We just said it is a highest priority where prevalence is high and the return rate is low. We are not trying to say that few people should use it, nor are we trying to indicate that everyone should jump to this immediately, because the number of false positives relative to true positives in a very-low-prevalence environment is potentially problematic."
In an appendix to one of its issue papers, the CDC lays out the positive predictive value of the SUDS test in populations with differing HIV prevalence. As an example, the CDC explains that if 1,000 patients were tested with SUDS at an STD clinic with a 10% HIV prevalence, one could expect 100 true-positive tests and four false-positive tests for a positive predictive value of 96% (i. e., 96 would be truly positive). The same test on 1,000 patients in a family planning clinic with a 0.4% prevalence would yield four true positives and four false-positive tests, for a positive predictive value of 50%.
The other consideration for a clinic in deciding on rapid HIV testing is evaluating the number of patients who don't return for tests. If the number is fairly low, implementing rapid testing could substantially increase operating costs because the SUDS rapid test kit ranges in cost from $6 to $10, compared to $1 to $2 for a standard EIA test, the CDC notes.
The adoption of rapid HIV testing can change the delivery of counseling and testing in several ways, according to the CDC papers. These include:
· There may be a higher number of those receiving a test, yet fewer return visits because most patients will test negative and will not need to return for their results as they have with EIA tests.
· Client visits may increase in length because specimens may be batched, forcing patients to wait several hours for their results, and counselors may spend more time with each client because two contacts will be required with each client.
· Rapid testing will require changes in how and when HIV prevention counseling is delivered. Although an interactive, personalized client risk assessment still will be needed, special attention will have to be given to ongoing behaviors and circumstances putting clients at risk of HIV, the CDC notes. Moreover, the probability of false-positive tests requires additional counseling to clients on the risks of false positives, CDC officials add.
Reference
1. Centers for Disease Control and Prevention. Update: HIV counseling and testing using rapid tests - United States, 1998. MMWR 1998; 47:211-215.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content