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5-hour biopsy processing program

Reviewing the Processing Steps

Surgical tissue is treated with various reagents (eg, alcohols and xylenes) to preserve tissue components and prepare the specimen for paraffin embedding and sectioning. The process is long and involved, and each sequential step is completely dependent on the previous one. The basic processing steps are outlined in order below:
  1. Fixation: Formalin stabilizes tissue proteins to prevent further changes, such as decay.
  2. Dehydration: Increasing concentrations of alcohol (70%, 95%, 100%) remove water from tissue.
  3. Clearing: Xylene or isopropanol removes dehydrant (alcohol) from tissue in preparation for paraffin infiltration; the clearant must be miscible (be able to mix) with the paraffin.
  4. Paraffin infiltration: Wax media displaces the clearing agent in tissue with paraffin, in preparation for paraffin embedding.
The chart on the right is an example of a five hour biopsy processing program on a closed-system processor with vacuum.