Dehydration of formalin-fixed specimens should begin with which alcohol concentration?

• A. 50-60%
• B. 65-70%
• C. 80-90%
• D. 90-100%

Answer: (B)

Gradual dehydration is used to gently replace water in fixed tissue with alcohol, preserving cellular detail and morphology. The first step should be a mid-range ethanol concentration because it begins removing water without pulling it out too quickly. About 65–70% ethanol contains enough water to allow diffusion and replacement of water in the tissue while avoiding sudden shrinkage or distortion that can occur with higher concentrations. Starting with a lower concentration (50–60%) would be too slow and leave excessive water; jumping to high concentrations (80–90% or 90–100%) can dehydrate too rapidly and compromise tissue structure. After this initial gentle start, the process proceeds through higher alcohols to complete dehydration before clearing and paraffin embedding.