What fixative is used for Mayer mucicarmine stain?

• A. 10% NBF
• B. Bouin's solution
• C. Ethanol
• D. Formalin

Answer: (A)

Mayer mucicarmine staining relies on preserving mucin so the dye can bind to the acidic mucopolysaccharides in the tissue. A fixative that maintains mucin integrity and keeps pH stable will yield reliable magenta staining of mucin with a clear hematoxylin counterstain for nuclei. Ten percent neutral buffered formalin does just that: it preserves tissue architecture and mucin without introducing the artifacts or extraction risks seen with other fixatives. Bouin’s solution contains picric acid, which can cause background staining and color shifts that interfere with the mucicarmine reaction. Ethanol is dehydrating and can extract mucin, reducing staining. Unbuffered formalin can have pH fluctuations that affect mucin preservation and staining consistency. Therefore, this buffered formalin is the preferred fixative before Mayer mucicarmine staining.