This Month's HIV/AIDS Facts

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Question: How good are the antibody tests?

Basic Answer: The standard tests that detect HIV antibodies are very good. The combination of the ELISA antibody test (the standard screening test) followed by the Western blot or IFA (confirmatory tests) is able to detect signs of HIV infection in almost 100 percent of HIV-positive blood, urine or fluid from the mouth.

Detailed Answer: The standard tests that detect HIV antibodies are very good. A sample of blood, urine or fluid from the mouth is screened for antibodies to HIV using the ELISA antibody test. If the ELISA detects HIV antibodies, the sample is tested again using another ELISA. If the second ELISA shows the same result, the sample is tested a third time using a confirmatory test. This test is usually either a Western blot or an IFA (indirect immunofluorescence assay). A sample is considered to be HIV infected when an ELISA showing the presence of HIV antibodies is repeated, with the same results, and then confirmed as positive by a Western blot or IFA. This testing method increases the accuracy of detecting HIV infection to almost 100 percent.

SOURCES:

• Centers for Disease Control and Prevention. MMWR, 2001; vol. 50, no. RR-19. "Revised Guidelines for HIV Counseling, Testing, and Referral."
• DeVita, V., Jr., et al., eds. AIDS: Etiology, Diagnosis, Treatment and Prevention, 4th ed. 1997.
• Journal of the American Medical Association, 1997; vol. 277, no. 3. "Evaluation of a System Using Oral Mucosal Transudate for HIV-1 Antibody Screening and Confirmatory Testing." Gallo, D., et al.

For current statistics, contact the CDC National AIDS Hotline (800/342-AIDS), Spanish (800/344-7432), TTY/TDD (800/243-7889); the CDC Voice and Fax Information System (888/232-3228); the CDC National Prevention Information Network (800/458-5231) or its Web site at www.cdcnpin.org; or the CDC HIV/AIDS Web site at www.cdc.gov/hiv/dhap.htm.