Which type of control material is inappropriate for Mayer mucicarmine staining?

• A. Autolyzed tissue
• B. Mucin-containing tissue
• C. Fresh tissue
• D. Paraffin-embedded tissue

Answer: (A)

Mayer mucicarmine staining highlights acidic mucins, turning them magenta. To reliably validate the stain, you need tissue where mucin is preserved through standard processing. Autolyzed tissue has undergone enzymatic breakdown after death, causing degradation of mucin and disruption of tissue structure. This makes staining results unpredictable and unreliable as a control, since you can’t trust whether a negative or weak signal is due to the stain or to degradation. In contrast, mucin-containing tissue provides the expected magenta mucin color and paraffin-embedded tissue, after proper fixation, preserves mucin well enough to serve as a valid positive/quality-control material. Fresh tissue is less ideal because it may not be fixed and processed consistently, which can affect mucin preservation, but the key issue with autolyzed tissue is the loss of mucin integrity that undermines a proper control.