Formalin fixed tissue shows very faded blue staining with the Masson trichrome technique. What is the most likely explanation?

• A. Left too long in the final acetic solution
• B. Left too long in the final base solution
• C. Not enough nuclear counterstain
• D. Staining reagents expired

Answer: (A)

In Masson trichrome, the blue color comes from the blue stain that marks collagen, with the acetic acid step used to differentiate and sharpen that blue. If the final acetic acid solution is left on too long, the blue dye can be leached out, washing away the blue and leaving very pale collagen staining. That precise overexposure to the acetic acid explains the faded blue appearance observed.

Other possibilities don’t fit as neatly. Extending time in the final base solution would alter colors differently and isn’t the typical cause of blue fading. Not enough nuclear counterstain would mainly affect the nuclei, not the intensity of the blue collagen stain. Expired reagents could weaken staining overall but wouldn’t specifically explain blue fading due to an overlong acetic acid step.