Which of the following is a likely cause of uneven staining and poor nuclear detail in H&E sections?

• A. Water in the clearing agent
• B. Over-staining
• C. Inadequate embedding
• D. Over-fixation

Answer: (A)

Uneven staining with blurred nuclear detail happens when the tissue isn’t cleared uniformly, so the paraffin infiltrates inconsistently. Water in the clearing agent prevents proper clearing, blocking complete replacement of alcohol and any residual water at the tissue surfaces. This leaves some areas less permeable to hematoxylin and eosin, producing mottled staining and nuclei that don’t take up stain evenly, which makes nuclear outlines look fuzzy.

Other options don’t fit this pattern as well. Over-staining tends to darken the section overall rather than create uneven staining or specifically blur nuclei. Inadequate embedding causes physical artifacts and section integrity problems more than a widespread, stain-penetration issue. Over-fixation can dull nuclear detail, but it’s usually more uniform and not the primary cause of patchy staining seen with poor clearing.