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

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Chemical Methods of End-point Determination

A less invasive method for determining the end of decalcification is through testing the decalcifying solution, rather than testing the tissue itself. This method is most often used with a formic acid decalcifier. If the testing solution turns cloudy, calcium is still being released and decalcification is not complete.
Chemical method:
  • Combine 5 mL of used decal solution + 5 mL ammonium hydroxide + 5 mL ammonium oxalate
  • Mix and wait 30 minutes
  • Calcium oxalate forms creating a cloudy precipitate if it has calcium to bind with
  • If solution is cloudy, tissue is still releasing calcium into decal solution
  • Decal solution should be changed and tissue should continue to decalcify
  • If solution is clear, decalcification is complete
  • This method is more accurate and less damaging than physical methods
  • DRAWBACK: Each piece of tissue must be decalcified separately to determine the individual end-point