March 27, 1998
In comparison, results from enzyme immunoassays (EIAs) currently used for HIV screening often are not available for 1-2 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 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, Georgia). 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and the HIV prevalence reported from publicly funded testing sites in the 1995 client record CT database (CDC, unpublished data, 1996).
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 (Table 1), 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 test4 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.
by testing site type United States, 1995
|Site type||HIV prevalence||HIV positive||HIV negative|
|HIV counseling and testing||1.9%||82.1%||84.3%|
|Sexually transmitted disease clinics||1.6%||67.8%||48.1%|
|Family planning programs||0.4%||76.9%||63.0%|
|Drug treatment programs||2.9%||73.6%||70.8%|
|Other testing sites*||2.1%||73.2%||64.6%|
*Prenatal clinics, tuberculosis clinics, community health centers, jails, hospitals, field visits, and unspecified sites.|
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 (Table 2). Approximately 2 million persons whose rapid-test results were negative would have learned their HIV status without a second clinic visit. An additional 8170 persons (22% of all positive tests performed in 1995) would have received confirmed positive results.
An additional 1115 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 sites such 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 test4.
Using the rapid test, 8301 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.
Reported by: Association of State and Territorial Public Health Laboratory Directors. Div of HIV/AIDS Prevention, Div of STD Prevention, National Center for HIV, STD and TB Prevention; Div of Environmental Health Laboratory Sciences, National Center for Environmental Health; Div of AIDS, STD, and TB Laboratory Research, National Center for Infectious Diseases; Div of Laboratory Systems, Public Health Practice Program Office, CDC.
Editorial Note: 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§ of rapid assays are comparable to those of EIAs.
Because HIV prevalence is low in most U.S. testing settings, the negative predictive value ¶ 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 prevalence3. Therefore, a reactive rapid test must be confirmed by a supplemental test5. 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 use6. However, only one rapid test approved by the Food and Drug Administration 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 testing4.
TABLE 2. Number of persons who would have learned their HIV-test results at publicly funded counseling and testing sites using rapid test and current HIV-testing strategies, and percentage difference between the strategies, by testing site type - United States, 1995
|Test results||Rapid test strategy||Current strategy||% Difference|
|Initial false positive||2,718|
|Initial false positive||2,224|
|Initial false positive||1,977|
|Initial false positive||951|
|Initial false positive||431|
|Initial false positive||8,301|
|* From the 1995 CDC client record counseling and testing database.|
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 ASTPHLD for reporting HIV-test results5.**
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 results5. However, they agreed that exceptions are warranted when the health benefit of reporting HIV-rapid-test results offsets the potential risk for reporting false-positive rapid-test results (e.g., 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 (e.g., 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 testing37. All persons with a first-time positive HIV-test result also should have another specimen collected and tested according to the currently recommended algorithm5.
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 client's risks4. When conveying a reactive rapid-test result, counselors should consider both the HIV prevalence in their setting and an assessment of each client's 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 (e.g., 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 (e.g., most practitioners' offices). Other settings require individual consideration. CDC, in collaboration with its prevention partners, is developing guidelines on the implementation and quality assurance of rapid 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 testing4.
When additional rapid tests become available for use in the United States, the PHS will re-evaluate algorithms using specific combinations of two or more rapid tests for screening and confirming HIV infection.
1. Kamb ML, Bolan G, Zenilman J, et al. Does HIV/STD prevention counseling work? Results from a multi-center randomized trial (Project Respect) [Abstract 0134] In: Program and abstracts of the International Congress of Sexually Transmitted Diseases. Seville, Spain: Association for Research in Clinical Microbiology, 1997:83.
2. CDC. HIV counseling and testing in publicly funded sites: 1995 summary report. Atlanta: US Department of Health and Human Services,
CDC, September 1997.
3. George JR, Schochetman G. Detection
of HIV infection using serologic techniques in AIDS testing: a comprehensive guide to technical, medical, social, legal, and management issues. 2nd ed. Schochetman G, George JR, eds. New York: Springer-Verlag, 1994.
4. Kassler WJ, Dillon BA, Haley C,
Jones WK, Goldman A. On-site, rapid HIV testing with same-day
results and counseling. AIDS 1997;11:1045-51.
5. CDC. Interpretation and use of
the Western blot assay for serodiagnosis of human immunodeficiency
virus type 1 infections. MMWR 1989;38(suppl
6. Stetler HC, Granade TC, Nuñez
CA, et al. Field evaluation of rapid HIV serologic tests for screening and confirming HIV-1 infection in
Honduras. AIDS 1997;11:369-75.
7. Kassler WJ, Haley C, Jones WK, Gerber AR, Kennedy EJ, George JR. Performance of a rapid, on-site human immunodeficiency virus antibody assay in a public health setting. J Clin Microbiol 1995;33:2899-902.
*Single copies of this report will be available until March 27, 1999, from CDC's National AIDS Clearinghouse, P.O. Box 6003, Rockville, MD 20849-6003; telephone (800) 458-5231 or (301) 519-0459.
of trade names is for identification only and does not imply endorsement
by CDC or the U.S. Department of Health
and Human Services.
§Sensitivity is the probability that the test result will be reactive if the specimen is a true positive; specificity is the probability that the test result will be nonreactive if the specimen is a true negative. ¶ The predictive value of a screening test is the probability that the test accurately predicts the true infection status of the person tested.
**Names of workshop participants are available from CDC's National AIDS Clearinghouse