What is the role of Western blot in HIV testing?

• A. Screening test
• B. Not used
• C. Confirmatory test after a positive screen
• D. Used only for HTLV

Answer: (C)

After an initial HIV screening test, a confirmatory test is used to be sure the result isn’t a false positive. Western blot fits this role because it detects antibodies to several specific HIV proteins, so a pattern of reactivity to multiple HIV components provides strong evidence of true infection. This higher specificity helps distinguish true positives from false positives that can occur with screening assays, making it the standard confirmatory step in many testing algorithms.

It’s not used as a screening test because screening aims for high sensitivity to catch as many true infections as possible, even at the cost of some false positives. It’s also not specific to HTLV; HIV testing relies on Western blot to confirm HIV status, often after an initial positive screen. In modern practice, some locations may use other confirmatory methods, but the concept remains: confirm infection after a positive screen.