CAP recommends including how many tissue samples in the antibody validation set?

• A. Minimum of 10
• B. Minimum of 15
• C. Minimum of 50
• D. Minimum of 25

Answer: (D)

Adequate sample size for antibody validation in immunohistochemistry relies on having enough tissue diversity to assess how the antibody performs across different contexts. CAP guidance requires a minimum of 25 tissue samples in the validation set so you can include tissues with known positive staining, known negatives, and a range of expression levels. This breadth helps reveal potential cross-reactivity and ensures scoring is reliable across samples. Using fewer samples risks missing tissue-specific effects or rare false positives, making validation less robust. While more samples can strengthen confidence, 25 is the standard minimum CAP specifies.