What fixative is used for fixation in routine processing?

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

Answer: (A)

Routine fixation aims to preserve tissue architecture in a way that’s compatible with paraffin processing and standard staining. The best choice for this purpose is 10% neutral buffered formalin. The neutral pH prevents acid-induced artifacts that can blur nuclear detail and alter antigenicity, while formaldehyde cross-links proteins to stabilize cellular structures. This combination provides reliable preservation that works well through dehydration, clearing, and embedding processes and yields crisp H&E staining.

Bouin’s fixative, while excellent for certain细细 aspects of morphology, contains picric acid and acetic acid and leaves a yellow pigment and can cause excessive distortion—making it unsuitable for routine paraffin processing and most immunohistochemistry. Alcohol fixes tissues by dehydration and precipitation rather than cross-linking, which often leads to tissue shrinkage and poor nuclear detail, so it isn’t ideal for routine paraffin sections. Plain formalin (unbuffered) can be more acidic and introduce artifacts, whereas the buffered form maintains a neutral environment and preserve morphology more consistently.

So, the routine fixative is 10% neutral buffered formalin because it provides stable, well-preserved tissue suitable for standard processing and staining.