When is validation of an IHC assay necessary?

• A. Only during initial development
• B. Every time you run a stain
• C. When introducing a new antibody, changing fixative, antigen retrieval, detection system, and instrumentation
• D. Only when using the same antibody

Answer: (C)

Validation is required whenever the assay components or workflow are changed because even small tweaks can alter performance, including what is detected and how clearly it’s seen. Introducing a new antibody can bring different binding characteristics and cross-reactivity; changing the fixative can affect how well tissue antigens are preserved; altering antigen retrieval methods changes epitope exposure; switching the detection system or instrumentation can modify signal strength and background. All of these potential shifts can impact accuracy, so a formal validation ensures the staining remains specific, sensitive, and reproducible under the new conditions.

The other scenarios don’t cover these fundamental changes: validating only at initial development misses later alterations; validating every single run is unnecessary and impractical because routine quality control handles daily performance; using the same antibody with the same protocol generally doesn’t require full re-validation, though ongoing controls are still important.