>From my Grossing Technology book:
Gouty tissue contains monosodium urate crystals. Tissue specimens with gout
diagnosis must be submitted in either Carnoy’s fixative (chloroform, acetic
acid, and absolute ethanol, now almost abandoned in regular practice) or in
absolute ethanol. Fixation cannot be in formalin, as formalin contains water
which may dissolve any urate crystals that are present (uric acid is even more
soluble in formalin than in water).
Once received, the specimen must be processed from 100% ethanol, skipping not
only formalin, but also the graded alcohol series in the tissue processor. Some
laboratories start with 70% alcohol in microwave-assisted processing. However,
urate crystals, particularly in large deposits (tophi), often survive formalin
fixation and routine processing anyway.
If a gout specimen is received in formalin, it can be recovered by drying the
fixative on a slide in an oven and mounting it unstained for Diff-Quick stain.
Unstained slide can be viewed under polarized light. By using red filter under
polarized light uric acid crystals can also be distinguished from calcium
pyrophosphate dihydrate crystals (pseudogout). The rest is in the
histotechnology realm.
Izak Dimenstein
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Subject: Histonet Digest, Vol 232, Issue 11
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