A section stained with Gomori reticulin stain and counterstained with nuclear fast red shows cloudiness of both the section and the slide. What is the most likely cause?

• A. Inadequate washing after nuclear fast red
• B. Overwashing after staining
• C. Excess counterstain
• D. Low pH mounting medium

Answer: (A)

Not removing residual counterstain after applying the nuclear fast red is the most likely cause. After the Gomori reticulin stain, the nuclear fast red is used to counterstain nuclei, and it should be thoroughly washed away. If washing is inadequate, excess dye can remain on the tissue and also migrate to the glass slide, producing a cloudy, hazy appearance over both the section and the slide. Overwashing would tend to wash away too much stain and make the section pale rather than cloudy. An excess counterstain would intensify nuclear staining but isn’t the typical reason for a blanket cloudiness across both tissue and slide. A mounting medium with a very low pH is unlikely to cause this specific cloudiness; it might cause other refractive or staining issues but not the general haziness produced by residual dye.