A Simple Method to Demonstrate Urate Crystals in Formalin Fixed Tissue

In clinically suspected cases of gout the surgical tissue specimens should be fixed in absolute ethyl alcohol, because urate crystals are soluble in aqueous formaldehyde. In clinically not recognized cases of gout surgical specimens are usually fixed in formalin in which urate crystals may dissolve. The aim of this study was to demonstrate the advantages of examining not staining sections under polarized light in comparison with haematoxylin-eosin stained ones viewed with normal light. One hundred twenty five (125) tissue samples of 30 patients with gout were studied in serial sections stained with haematoxylin-eosin (examined by usual light microscope), or were studied in unstained sections (examined under polarized light) with an Olympus BX51 polarization microscope. Urate crystals were demonstrable in 23.3% of formalin fixed tissue specimens of the patients stained with haematoxylin-eosin but were present in 56.7% of not stained tissue section viewed under polarized light. Urate crystals were demonstrable in 43.7% of formalin fixed tissue specimens which were considered negative with haematoxylin-eosin stain. The authors concluded that in case of gout the tissue specimens are best evaluated in sections stained with haematoxylin-eosin and in unstained sections as well. The probability of urate positive microscopic findings is significantly higher (c²=4.8700, p<0.027) in unstained sections viewed under polarized light than in the haematoxylin-eosin stained ones. This approach may also be useful in other crystal deposition induced diseases.