Which statement best describes the interpretation basis for qualitative IHC results?

• A. By the number of positive cells alone
• B. By the standard staining protocol duration
• C. By the correct cellular localization of the staining reaction and staining of the correct tissue structures
• D. By the overall color tone of the slide

Answer: (C)

Interpreting qualitative IHC results hinges on where the stain appears, not how much staining you see. A true qualitative positive is defined by staining in the correct cellular compartment (for example, nuclear for a transcription factor, membrane for a receptor, or cytoplasmic for certain enzymes) and within the appropriate tissue structures. This subcellular and architectural localization confirms that the antibody is binding the intended antigen in the right cellular context, rather than producing random background signal. Relying on the number of positive cells or the overall color tone can be misleading, and the duration of the staining protocol is not what determines the interpretation. Staining that localizes to the wrong compartment or to non-target structures suggests non-specific or artifactual signal, even if some color is visible.