Which fixative is specifically suitable for demonstrating urate crystals when used as the primary fixative?

• A. Absolute alcohol
• B. Formalin
• C. Bouin
• D. Zenker

Answer: (A)

When urate crystals are the target, the fixative should preserve the crystals without dissolving them. Urate crystals are soluble in aqueous fixatives, so fixatives that contain water tend to dissolve or alter the crystals and obscure their appearance. Absolute alcohol, being non-aqueous, fixes tissue while dehydrating and precipitating the crystals, keeping them in place and visible for demonstration (often under polarized light). In contrast, formalin, Bouin, and Zenker are aqueous or contain components that interact with or dissolve crystals, making them less reliable for showing urate crystals as the primary fixative.