|
The Multispot rapid test is FDA-cleared to distinguish HIV1 and HIV2.
- Technical or clerical error
FALSE POSITIVE RESULTS: The frequency of false positive HIV serology (both EIA and WB) was reported to range from 0.0004% to 0.0007% (JAMA 1998;280:1080; Arch Intern Med 2003;163:1857; Arch Intern Med 2000;160:2386). The .0004% rate is based on a report from the Red Cross showing 20 false positives among 5.02 million donations from 1991-95 or 1/21,000 (JAMA 1998;280:1081). Of the 20,18 (90%) had a WB pattern showing envelop +/- one additional band only. Important clues to possible false positive tests are lack of risk factors, undetectable viral load, and normal CD4 count (Arch Intern Med 2003;163:1857). The serologic test should be repeated in patients without other laboratory evidence of infection. Causes of false-positive results include:
- Autoantibodies: A single case was reported in which a falsepositive serology was ascribed to autoantibodies (NEJM 1993;328: 1281), but a subsequent report indicated that this patient did have HIV infection as verified by positive cultures (NEJM 1994;331:881).
- HIV vaccines: HIV vaccines are the most common cause of false positive HIV serology. In an analysis of 266 healthy volunteers in HIV vaccine studies, 68% had positive EIA tests, and 0% to 44% had positive WB, depending on the antigen used in the vaccine (Ann Intern Med 1994;121:584).
- Factitious HIV infection: This refers to patients who report a history of a positive test that is erroneous, due to either misunderstanding or an intent to deceive (Ann Intern Med 1994;121: 763). It is important to confirm anonymous tests and to repeat laboratory reports that cannot be verified, using either repeat serology or viral load testing. Note that 2 to 9% of VL tests are falsely positive, usually with low viral titers (Ann Intern Med 1999;130:37).
- Influenza vaccination: Any brand of influenza vaccine may cause false positive screening results for HIV-1, presumably due to homology in their envelope proteins (Am J Epidemiol 1995;141: 1089; NEJM 2006;354:1422; Cell 1997;89:263).
- Technical or clerical error (Arch Intern Med 2003;163:1857)
INDETERMINATE RESULTS: Indeterminate test results account for 4% to 20% of WB assays with positive bands for HIV-1 proteins. Causes of indeterminate results include:
- Serologic tests in the process of seroconversion; anti-p24 is usually the first antibody to appear.
- Late-stage HIV infection, usually with loss of core antibody.
- Cross-reacting nonspecific antibodies, as seen with collagenvascular disease,
|
