In immunodiagnostics, what is the purpose of confirming ELISA results with Western blot?

• A. To replace ELISA due to lower cost.
• B. To quantify the same antigen with higher precision.
• C. To measure cell surface markers.
• D. To provide confirmatory specificity after an initial ELISA.

Answer: (D)

Screening ELISA is designed to be highly sensitive, so it can catch most true positives, but it can produce false positives from cross-reactivity or nonspecific binding. Western blot adds a second layer of specificity by separating proteins, transferring them to a membrane, and testing whether patient antibodies bind to a defined set of individual proteins. A true positive pattern shows antibodies against multiple specific antigens at expected weights, which confirms the initial result and reduces the chance of a false positive. That’s why this step is used as a confirmatory test after ELISA. It isn’t about replacing ELISA or measuring the same antigen with higher precision, nor about assessing cell surface markers.