Why Provide Rapid HIV Testing?
Approximately 2.1 million HIV tests are conducted annually in publicly funded counseling, testing, and referral (CTR) programs. However, many persons do not return for the results of standard tests: 30% of persons who tested HIV-positive during 2000 and 39% of persons who tested HIV-negative did not return.1
Almost all clients receive their rapid HIV test results because results can be provided immediately during the testing visit.
How Do Rapid HIV Tests Compare With Standard HIV Screening Tests, Enzyme Immunoassays (EIAs)?
Clinical studies have demonstrated that the sensitivity2
and the specificity3
of rapid HIV tests are comparable to those of EIAs often used for screening. The negative predictive value4
of a screening test is high at the HIV prevalence observed in most U.S. testing settings (CDC, 1998). Therefore, a client with a negative rapid HIV test result can be told he or she is not infected. However, because HIV antibodies take time to develop, retesting should be recommended to persons with a recent possible exposure (sexual contact or needle sharing within 3 months). As with any screening test, the positive predictive value of a reactive rapid HIV test may be low in populations with low prevalence (see Appendix
). Because some reactive test results may be false-positive, every reactive rapid test must be confirmed by a supplemental test (either Western blot or immunofluorescence assay [IFA]). (CDC, 1989).
HIV Counseling With Rapid HIV Tests
HIV counseling encompasses two components: provision of information and prevention counseling (CDC, 2001a). All clients must receive information about the rapid test and give informed consent for testing. Clients who can benefit should also receive prevention counseling.
Information can be provided either in a face-to-face meeting with a counselor or in a pamphlet, brochure, or video. Clients tested with a rapid HIV test should be given the same types of information recommended for those tested with a standard EIA:
- Information about the HIV test, its benefits and consequences.
- Ways HIV is transmitted and how it can be prevented.
- The meaning of the test results in explicit, understandable language.
- Where to obtain further information and, if applicable, HIV prevention counseling.
- Where to obtain other services including, if applicable, treatment.
In addition, clients tested with rapid HIV tests should be
- Advised that their rapid test results will be available during the same visit.
- Informed that confirmatory testing is needed if the rapid test result is reactive.
Communicating the Meaning of the Rapid HIV Test Results
Negative Rapid HIV Test Results
During the initial visit, the provider can definitively tell clients whose rapid HIV test result is negative that they are not infected, unless they have had a recent (within 3 months) known or possible exposure to HIV. Retesting should be recommended for these clients because sufficient time needs to elapse in order before antibodies develop that can be detected by the test.
Reactive (Preliminary Positive) Rapid HIV Test Results
Further testing is always required to confirm a reactive (preliminary positive) screening test result.
Providing reactive (preliminary positive) results to clients without the benefit of a same-day confirmatory test can be a challenge. For all clients with a reactive rapid HIV test result, however, it is essential to:
- Explain the meaning of the reactive test result in simple terms, avoiding technical jargon.
- Emphasize the importance of confirmatory testing and schedule a return visit for the confirmatory test results.
- Underscore the importance of taking precautions to avoid the possibility of transmitting infection to others while awaiting results of confirmatory testing.
A simple message to convey this information could be "Your preliminary test result is positive, but we won't know for sure if you are infected with HIV until we get the results from your confirmatory test. In the meantime, you should take precautions to avoid transmitting the virus."
HIV Prevention Counseling
Fundamentals of HIV prevention counseling with rapid HIV tests include:
- Keep the session focused on HIV risk reduction.
- Include an in-depth, personalized risk assessment.
- Acknowledge and provide support for positive steps already made.
- Clarify critical rather than general misconceptions about HIV risk.
- Negotiate a concrete, achievable behavior-change step that will reduce HIV risk.
- Seek flexibility in the counseling technique and process, avoiding a "one-size-fits-all" approach.
With standard testing, there are always two test-associated opportunities for prevention counseling for clients who return for their results. With rapid testing, there may be either one or two.
- Clients with preliminary positive rapid HIV test results also have two test-associated opportunities -- one on the day of testing and one when they return for their confirmatory results.
- Clients with HIV-negative rapid HIV test results usually have only one test-associated opportunity. They will not have an opportunity to try out their risk-reduction plan or to discuss with the counselor their attempts at carrying it out before they receive their HIV result. However, at the visit when the rapid testing is done, if the counselor thinks that the client's risks warrant additional prevention counseling after negotiating and discussing a risk-reduction step, he or she can schedule a second appointment with the client for this purpose.
HIV prevention counseling with a rapid HIV test completed in a single visit has been successfully implemented in several settings in the United States over the past several years with the SUDS (Single Use Diagnostic System for HIV-1) rapid test. Experience has shown that this form of prevention counseling is feasible and is well accepted by most clients and counselors. An example of a counseling protocol for providing prevention counseling during one visit for clients receiving rapid test results and materials for counselors can be found at the RESPECT-2 web site. The OraQuick test may introduce some differences, because, unlike the SUDS test (which is sent to the lab) it may be possible for the counselor both to perform the test and to provide the counseling,
Future of Rapid HIV Testing
Several other rapid HIV tests already being used outside the United States will likely be considered for FDA approval. Many of these tests require a single step, can be performed on whole blood, serum, plasma, oral fluid, or finger-stick blood samples, and provide results within minutes. These tests also have a high sensitivity and the specificity (Branson, 2000). When these tests become available, it may be possible to implement strategies such as one recommended by the World Health Organization (WHO, 1997) whereby specific combinations of different rapid tests might be used to confirm reactive rapid HIV test results immediately.
Appendix: Positive Predictive Value of Rapid HIV Tests
Positive predictive value is an important concept that may be difficult to understand. It depends both on the test that is used (in particular, the tests specificity) and the prevalence of infection in the population tested. An example may help to illustrate how the positive predictive value (and the proportion of false-positive test results) changes at different levels of prevalence.
We will illustrate a test that has a sensitivity of 99.9% and a specificity of 99.8%, similar to that of many rapid HIV tests and EIAs. A specificity of 99.8% means that 0.2% (2 tests out of 1,000) will be false-positive. For this example, we will test 1,000 persons, first in an STD clinic with high HIV prevalence: 5%. Testing 1,000 persons, we would discover 50 persons who were truly positive. Based on the tests specificity, we would also encounter 2 false-positive test results. Thus, the positive predictive value of a reactive test in this setting would be (50 true positive tests) divided by (52 total positive tests) or 96%.
Using this same test in a population with low prevalence gives us a very different predictive value. For this example, we will use the same test in a family planning clinic, where the HIV prevalence is 0.1%. Testing 1,000 persons in this clinic, 1 person would be truly positive, but again, 2 test results would be false-positive. The positive predictive value of a reactive test in this setting, therefore, would be (1 true positive test) divided by (3 total positive tests) or 33%. Notice that in both these examples, the number of false-positive tests is the same, but the proportion of false-positive tests is very different.
The following table shows the positive predictive values at different levels of HIV prevalence for a test with 99.8% specificity.
|Positive Predictive Value of HIV Tests in Populations With Differing HIV Prevalence |
Example: Testing 1,000 Persons
|HIV Prevalence ||True Positive |
| False Positive |
- HIV CT Client Record Report, 2000 U.S. Total; CDC, unpublished data.
- 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 negative if the specimen is a true negative.
- The predictive value of a screening test is the probability that the test result predicts the true infection status of the person tested.