Skin punch biopsy: how and where to take it
7-year-old cat with pustules and yellowish crusts on the bridge of the nose, around the eyes and on the inner pinnae, plus paronychia. You are going to take biopsies for histopathology.
Which biopsy technique is correct?
chevron_right Show answer and explanation
A. Prepare the site with chlorhexidine and alcohol, as for surgery, before the punch
Scrubbing and disinfecting removes crusts and the stratum corneum, which may hold the diagnostic clue (for example acantholytic keratinocytes or organisms). Clipping the hair with scissors is enough.
B. Choose the oldest, ulcerated lesions, because they show the most advanced disease
Ulcers and chronic lesions have secondary changes (fibrosis, infection, non-specific inflammation) that mask the primary process. Recent, primary lesions are preferred.
C. Give prednisolone for 2 weeks beforehand to reduce inflammation and obtain a cleaner sample
It is the opposite: corticosteroids alter the histological pattern and may prevent diagnosis. Ideally they should be withdrawn several weeks beforehand if the animal's condition allows.
D. Without scrubbing, clip the hair, take 3 or more 6 mm punches from recent lesions keeping the crusts, and fix in 10% formalin
Correct. Several samples of primary lesions (pustules, papules, recent crusts) increase the yield. Inject the local anaesthetic subcutaneously, not intradermally; handle the sample by the fat without crushing it, and send loose crusts in the same pot with about 10 times their volume of formalin.
lightbulb Key takeaway
Centre the punch on the lesion; for an ulcer or a pigment change, an elliptical scalpel biopsy including the edge lets the pathologist see the transition. Always send a good clinical history and list of differentials: interpretation depends on it.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.