Approximately 25 million persons each year in the United States are tested for antibody to human immunodeficiency virus (HIV). Publicly funded counseling and testing (CT) programs conduct approximately 2.5 million of these tests each year.
Approximately 25 million persons each year in the United States are tested for antibody to human immunodeficiency virus (HIV). Publicly funded counseling and testing (CT) programs conduct approximately 2.5 million of these tests each year. Computed tomography can have important prevention benefits; however, in 1995, 25% of persons testing HIV-positive and 33% of persons testing HIV-negative at publicly funded clinics did not return for their test results.
Rapid tests to detect HIV antibody can be performed in an average of 10 minute, enabling health-care providers to supply definitive negative and preliminary positive results to patients at the time of testing, potentially increasing the overall effectiveness of CT. In comparison, results from enzyme immunoassays (EIAs) currently used for HIV screening often are not available for 1 to 2 weeks. To quantify the potential advantages and disadvantages of using rapid tests for CT, CDC estimated the potential impact on the number of persons who would learn their HIV-test results. This report summarizes the results of the analysis and provides the basis for changing the Public Health Service (PHS) recommendations for providing HIV-test results.a
A decision model was designed to compare the current HIV-CT procedure and a strategy using the commercially available rapid test (Single Use Diagnostic System [SUDS] HIV-1 Test, Murex Corporation, Norcross, Georgiab). The analysis was based on the number of tests performed and the HIV prevalence reported from publicly funded testing sites in the 1995 client record CT database. The number of persons who would learn their true HIV status under each strategy and the number who would receive a preliminary false-positive rapid-test result were calculated using the HIV prevalence at different types of testing sites, the percentage of those who received results at each site type, and the published sensitivity and specificity of the EIA and the rapid test.
The client record database was used to determine the proportion of persons who received their HIV test results under the current strategy. Data from clinical trials were used for the percentage of persons who learned their HIV status after the rapid test. The small number of tests that would yield indeterminate results were included as HIV-positive results by assuming that confirmatory tests performed after repeatedly reactive screening tests were 100% specific.
Results of the Comparison
Using the rapid test, during 1995, a total of 697,495 more persons would have learned their HIV status, an increase of 29% for HIV-positive persons and of 50% for HIV-negative persons over the current CT procedure. Approximately 2 million persons whose rapid-test results were negative would have learned their HIV status without a second clinic visit. An additional 8,170 persons (22% of all positive tests performed in 1995) would have received confirmed positive results. An additional 1,115 HIV-infected persons who did not return for confirmed results would have been given a reactive rapid-test result and received counseling about the likelihood of being infected and the need for behavioral changes.
The benefits of using the rapid test were greatest at such sites as sexually transmitted disease (STD) clinics, where the lowest percentage of persons return for results. However, a substantial increase also was observed for voluntary HIV-CT sites, where > 80% of persons return. Clinical trials suggest an additional benefit for confidential testing sites: The proportion of HIV-positive persons who received results only after outreach efforts declined from 34% under the current procedure to 3% with use of the rapid test.
Using the rapid test, 8,301 HIV-negative persons would have received preliminary false-positive results after a reactive rapid test, representing 0.4% of the 2.1 million persons tested for HIV but 18% of those who would have received an initial reactive result. Most (97%) would have returned to learn their confirmatory test result was negative. Because of the differences in HIV prevalence at different types of testing sites, the proportion of persons given a reactive rapid-test result who were truly positive ranged from 46% at family planning clinics to 88% at drug-treatment programs.
Editorial Note From the CDC
The findings in this report indicate that use of a rapid test with same-day results for HIV screening in clinical-care settings can substantially improve the delivery of CT services. Because most persons who are tested are not infected, they can receive counseling and learn their HIV status in a single visit. In addition, providing preliminary positive results also increases the number of infected persons who ultimately learn their infection status and can be referred for medical treatment and additional prevention services.
The sensitivity and specificity cof rapid assays are comparable to those of EIAs. Because HIV prevalence is low in most US testing settings, the negative predictive valued of a single rapid test is high. A negative rapid test does not require further testing, and negative results with result-specific counseling can be provided to most persons at the initial visit. However, because the predictive value varies with the prevalence of HIV infection in the population tested, the positive predictive value of a test will be low in populations with low prevalence. Therefore, a reactive rapid test must be confirmed by a supplemental test.
In studies conducted outside the United States, specific combinations of two or more different rapid HIV assays have provided results as reliable as those from the EIA/Western blot combination that is in widespread use. However, only one rapid test approved by the FDA is commercially available in the United States. Therefore, persons whose rapid-test result is reactive can be counseled about their likelihood of being infected with HIV, but they must return for definitive results. Using a rapid HIV test increases the number of HIV-infected persons who learn they are infected, because more persons return for confirmatory results and counseling when they receive a preliminary positive result than when no result is provided until after confirmatory testing.
The CDC and the Association of State and Territorial Public Health Laboratory Directors (ASTPHLD) conducted a workshop in Atlanta on October 24, 1997, to discuss rapid HIV testing, the potential health benefits and risks of reporting provisional rapid-test results, and the feasibility of changing the recommendations of the PHS and ST-PHLD for reporting HIV-test results.e Workshop participants agreed that it is optimal to follow the 1989 PHS algorithm for HIV testing, which recommends confirmatory testing before reporting reactive HIV-test results to minimize the risk for reporting false-positive results. However, they agreed that exceptions are warranted when the health benefit of reporting HIV-rapid-test results offsets the potential risk of reporting false-positive rapid-test results (eg, patients who fail to learn their HIV status because they do not return to receive their test results). Rapid HIV tests also can assist health-care providers who must make immediate decisions about initiating HIV prophylaxis (eg, caring for health-care workers after occupational exposures and for pregnant women in labor who have not been tested or whose results are not available).
Health-care providers who choose to give patients test results from rapid HIV tests must ensure both high-quality testing and appropriate counseling. The laboratory must institute rigorous quality control and quality assurance plans, including participation in proficiency testing. All persons with a first-time positive HIV-test result also should have another specimen collected and tested according to the currently recommended algorithm.
Counseling clients about the likelihood that their result represents their true HIV-infection status is a critical adjunct to high-quality testing. Such counseling should emphasize the importance of confirmatory testing. When explaining a reactive HIV rapid test to patients, counselors have used phrases such as "a good chance of being infected" or "very likely infected" to communicate the probability of infection, and further qualified these phrases on the basis of an individual assessment during counseling of the clients risks. When conveying a reactive rapid-test result, counselors should consider both the HIV prevalence in their setting and an assessment of each clients individual risks.
Decisions about whether to use rapid tests should be based on a combination of the prevalence of HIV in a community and return rates for test results. For example, in settings of high prevalence where a low percentage of persons return for their results (eg, STD clinics), use of rapid tests will be most beneficial. In comparison, rapid tests may be less beneficial in settings of low prevalence where return can be ensured (eg, most practitioners offices). Other settings require individual consideration. The CDC, in collaboration with its prevention partners, is developing guidelines on the implementation and quality assurance of rapid HIV testing.
An Alternative Approach to HIV Testing
On the basis of the findings in this report and from the workshop, the PHS recommends an alternative approach to HIV testing: Health-care providers should provide preliminary positive test results before confirmatory results are available in situations where tested persons benefit. This recommendation is based on research demonstrating that persons who receive preliminary results understand the meaning of the result and prefer rapid testing. When additional rapid tests become available for use in the United States, the PHS will reevaluate algorithms using specific combinations of two or more rapid tests for screening and confirming HIV infection.
Adapted from Morbidity Mortality Weekly Report 47(11):211-215, 1998.