SF AIDS Fdn: AIDS 101 -- HIV Testing

SF AIDS Fdn: AIDS 101 -- HIV Testing: "The high sensitivity of the test creates a slightly lower specificity. This means the result could (infrequently) be 'false positive.' To compensate for this, confirmatory tests are automatically performed after a positive ELISA. The WB and IFA are highly specific for HIV antibodies, so they rule out false positive ELISAs nearly every time.
The CDC states that the combined accuracy of the ELISA plus either the WB or IFA is greater than 99%.
The CDC recommends retesting any positive ELISA twice; if either retest is positive, then a confirmatory test is performed. Only when the confirmatory test is also positive is the result reported as HIV positive. Again, reputable test sites automatically follow this procedure, so results reported to you can be relied upon completely."