A patient suspected of having human immunodeficiency virus (HIV) tests positive on an enzyme-linked immunosorbent assay (ELISA). The nurse understands that
• Testing for HIV using the immunoabsorbent assay (ELISA) can rule out HIV but may produce false positives that require further investigation. The test has a high sensitivity but low specificity, meaning a negative result indicates the absence of disease but a positive result often but not always indicates the presence of disease.
• Laboratories first screen for infection with a combination antigen/antibody immunoassay that detects HIV-1 and HIV-2 antibodies. No further testing is required for specimens that are nonreactive (negative).
• Specimens with a reactive result should be tested with another antibody immunoassay, followed by the Western blot.
• The Western blot is the test which is used to confirm diagnosis so treatment can begin.