The page below is a sample from the LabCE course Basic Tissue Orientation and Paraffin Embedding Technique. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Basic Quality Control

  • Histologists must practice to be able to rapidly identify and orient specimens during paraffin embedding. Taking too long to manipulate and position the specimen may cause more than one layer of solidified paraffin to form when molten paraffin is added to paraffin that has solidified in the bottom of the base mold. These separate layers may pull apart during microtomy or storage.
  • Pieces of all types should be placed with intention, in one plane, and not just randomly in the block face. Careless positioning will make it very unlikely that a single representative section can be easily obtained.
  • Correct by re-embedding, any gross defects such as cracks or air bubbles.
  • Observe the specimen for processing issues, such as poor fixation, dehydration, or infiltration.
  • A "white-ish" appearing or "mushy" texture due to inadequate dehydration in a processed tissue block is most likely in need of reprocessing. Submit this block for reprocessing prior to embedding; it is much easier to take the specimen back through these steps for correction now than to work backward from the final cut block.
  • Document and correct labeling discrepancies, illegible blocks, or incompleteness of cases during embedding, rather than "passing" these problems on to the microtomy step.

Paraffin block (top view) showing inadequate paraffin level.

Paraffin block with a large defect due to air being trapped inside by failure to add an inadequate paraffin.