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Laboratory Diagnosis of HIV Infection


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HIV Serologic Screening Algorithm

Slide 7

October 2009

Next, I will go through the HIV Serologic Screening and Supplemental Testing Algorithm. You can see in the top of this flowchart, that the Mayo Medical Laboratories test #9333 is a screening evaluation for HIV-1 and -2 antibodies. If that is reactive, it is automatically reflexed to HIV-1 antibody supplemental test by Western blot. From that test, one could see possibly 4 test results. Either positive, which means confirmed HIV-1 infection, or negative, which means that it’s truly negative or could be an HIV-2 infection giving the initial HIV-1 and -2 antibody screen results. Or, it could be an indeterminate or uninterpretable Western blot result, indicated in the gray box in the middle.

If the HIV-1 antibody confirmation by Western blot is negative in this testing algorithm, at Mayo Medical Laboratories, we automatically reflex to HIV-2 antibody-only screen. And if that is negative, then we recommend repeating serologic HIV testing starting from the HIV-1 and -2 antibody screen algorithm in 1 to 3 months for high-risk individuals. If the HIV-2 antibody screen is positive, then it’s recommended that we proceed to HIV-2 antibody supplemental test by immunoblot and that is done automatically on antibody screen-reactive specimen and, if that immunoblot assay result is negative, again we recommend HIV-2 antibody screen in 1 to 3 months, if clinically indicated.

For Western blot results that are indeterminate or uninterpretable, 2 tests are performed automatically. One is the HIV-2 antibody screen indicated by #86702, and also the #81758 HIV-1 antibody supplemental test by immunofluorescence. The reason for immunoflorescence test is to give provider additional assurance that we’re not missing an early HIV-1 infection that may be missed by the Western blot, since the immunofluorescence is also an FDA-approved supplemental test for HIV-1 antibody detection.

Based on the immunofluorescence test result, one could see a negative or a positive result. There’s also an additional option that the laboratory or provider could seek further confidence in an indeterminate or uninterpretable test result for Western blot and that is to proceed to HIV-1 proviral DNA qualitative detection by PCR Mayo Medical Laboratories #88635. And that is a research use only test and that can be positive or negative and then, depending on whether the individual is at high risk or low risk, the recommendation is indicated on the right-hand side of this testing algorithm.

HIV Serologic


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