What makes a reliable tissue control?

• A. Antigen expression must be unpredictable between independent samples
• B. Antigen expression must be predictable and stable between independent samples
• C. Controls should change with lot-to-lot variation
• D. Control must be negative for all antigens

Answer: (B)

The key idea is that a reliable tissue control must show known, constant antigen expression across different samples and runs. When the control’s antigen expression is predictable and stable, you have a dependable reference to confirm that the staining procedure—including fixation, antigen retrieval, and detection—worked correctly. This stability lets you distinguish a true negative in a patient sample from a technical failure, because the control should consistently stain as expected if the assay is functioning.

If the control’s antigen expression were unpredictable between independent samples, you wouldn’t be able to tell whether a negative result came from the sample or from the control itself, making the control unreliable. If the control varied with lot-to-lot changes, it wouldn’t provide a stable benchmark across runs. And a control that is negative for all antigens wouldn’t validate the assay’s ability to detect the targets of interest.