No further testing is needed for this patient, who does not have HIV infection. The fourth-generation antigen/antibody combination assay, which evaluates for the presence of HIV antibodies and the p24 viral nucleic acid protein, is recommended for initial HIV testing. This patient's initial testing was reactive, so further testing was indicated. The preferred follow-up testing for a positive result on an antigen/antibody combination assay includes an HIV-1/HIV-2 antibody differentiation assay and HIV nucleic acid amplification testing (NAAT) if the antibody differentiation assay finding is indeterminate or negative. HIV-1/HIV-2 antibody differentiation assay can identify the presence of HIV-1 or HIV-2 antibodies in the serum; HIV NAAT can detect viral RNA and is used to rule out the antibody-negative “window period” of acute HIV infection. Despite her initial positive test results, both follow-up test results were negative, and the appropriate interpretation is that her initial positive result on the screening test was a false positive. Although the recommended initial screening test has a reported specificity of 99.6%, in persons at low risk with very low pretest probability, the rate of false-positive results may still be significant. If the patient is at low risk and has no symptoms to suggest acute HIV infection, she should be reassured that the initial test result was a false positive (on the basis of her negative follow-up testing) and she does not have HIV.
T-cell subsets should never be used in diagnostic testing for HIV infection because a reduced CD4 cell count is neither sensitive nor specific for HIV infection.
Western blot testing for HIV antibody is no longer recommended for confirmatory testing of immunoassay results because of a higher risk for false-negative or indeterminate results early in the course of HIV infection.
Repeating HIV screening testing is unnecessary because the antibody differentiation immunoassay and NAAT have already clarified that the result of the initial combination assay was falsely positive. Repeating this study is therefore not indicated.