After completion of an IHC stain, background staining is observed in both control tissue and specimen tissue. Which of the following could be a cause?

• A. Excessive incubation with substrate-chromogen reagent.
• B. Reagents too concentrated.
• C. Sections incorrectly dewaxed.
• D. Slides inadequately rinsed.

Answer: (D)

Background staining in IHC happens when nonspecific binding or leftover reagents remain on the slides, so color develops in areas that shouldn’t have the target antigen. Proper rinsing is essential to remove unbound antibodies and to stop the chromogenic reaction; if rinsing is inadequate, unbound reagents stay on both control and test tissue, producing diffuse background staining across all sections.

So, when both control tissue and specimen tissue show background after staining, the most likely issue is slides not being rinsed well enough. Other options could contribute to stronger signal or nonspecific color, but they’re less directly tied to background appearing in every sample because of leftover, unremoved reagents.