When the presence of calcium was not expected, such as in kidney, lung, prostate, or skin tissue, but is revealed during trimming, paraffin-embedded tissue can be "surface decalcified" prior to microtomy. Also, bone that has already been decalcified may need more time in a decal solution, and surface decal may also be employed in such cases. Surface decalcification allows the decalcifier to penetrate a small distance into the block and dissolve the calcium.
Steps for surface decalcification of paraffin-embedded tissue blocks:
- Coarse face the tissue block to expose the entire tissue (if possible).
- Place the tissue block in the preferred decalcifier (typically HCl) for 30–60 minutes.
- Rinse the block in water and blot dry.
- Place on ice.
- Section as usual, but remember that only the surface was decalcified. Deeper sections may need to be decalcified.
