Which paraffin step uses vacuum during processing?

• A. Paraffin 1.5 hr (vacuum)
• B. Paraffin 30 min (no vacuum)
• C. Paraffin 1 hr (no vacuum)
• D. Xylene 1 hr (only vacuum)

Answer: (A)

Vacuum-assisted infiltration helps remove trapped air and enhances paraffin penetration into tissue. By applying vacuum during the paraffin step, wax can more thoroughly displace air and infiltrate dense or larger specimens, reducing voids and embedding artifacts. The 1.5-hour paraffin step done under vacuum provides sufficient time for complete infiltration, making it the step where vacuum is used. Shorter paraffin steps without vacuum won’t maximize penetration, and the xylene step isn’t a paraffin step, so vacuum there isn’t addressing the question.