What paraffin section thickness is used for Toluidine Blue mast cell staining?

• A. 4-5 micrometers
• B. 2 micrometers
• C. 6-8 micrometers
• D. 8-10 micrometers

Answer: (A)

Mast cell granules contain highly sulfated glycosaminoglycans that produce a metachromatic reaction with toluidine blue. For this metachromatic staining to be crisp and easy to interpret, the tissue needs to be thin enough for the dye to penetrate evenly but thick enough to preserve granule integrity and tissue morphology. Four to five micrometers in paraffin sections provides that balance: it allows uniform staining of the granules and clear visualization of the metachromatic color, while avoiding the tearing or folding risks of ultra-thin sections or the diffusion issues seen with thicker sections. Therefore, 4-5 μm is the optimal thickness for Toluidine Blue mast cell staining.