[Histonet] Histonet Digest, Vol 232, Issue 11

[Izak Dimenstein]

>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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