Which of the following describes the function of using separate high-expression and low-expression controls in IHC?

• A. High Exp- evaluate the process (right antibody)
• B. Low Exp- evaluate the sensitivity (right protocol)
• C. Non Exp- evaluate specificity (right signal to noise)
• D. Variation- required to evaluate robustness and correctness of staining result

Answer: (A)

Using a tissue with high antigen expression as a positive control checks that the staining process itself is functioning with the chosen antibody. If the high-expression control shows strong, expected staining, you know the antibody binds its target and the detection system and protocol are working properly. This validates that the overall process—the antibody binding, antigen retrieval, and detection steps—is capable of producing a signal when the antigen is abundant. Low-expression controls, on the other hand, probe how sensitive the assay is to detect lower antigen levels, while other controls address specificity or robustness. So this control setup best describes confirming the process with the right antibody.