Cytology smears should be fixed in which fixative?

• A. Osmium tetroxide
• B. Formalin
• C. Glutaraldehyde
• D. Methanol

Answer: (A)

Fixation for cytology smears aims to immobilize cellular structures quickly while preserving nuclear detail and staining characteristics. Alcohol-based fixatives, especially methanol, are preferred because they fix proteins rapidly, preserve both cytoplasmic and nuclear morphology, and are directly compatible with common cytology stains like Papanicolaou and Diff-Quik. Formalin and glutaraldehyde are strong aldehyde fixatives better suited to tissue sections and electron microscopy; they can cross-link proteins in ways that obscure details and interfere with routine cytology staining. Osmium tetroxide is a heavy-metal fixative used mainly for electron microscopy to preserve lipids and membranes, not for routine light-m microscopy cytology, and it is hazardous. So for standard cytology smears, methanol-based fixatives are the appropriate choice.