Comparison of Polarized Light Microscopic Findings of Synovial Fluid from a Joint with Gout and a Joint with Pseudogout.
|Crystal||Urate||Calcium pyrophosphate dehydrate|
|Shape||Needle||Rhomboid or rectangular|
|Color of crystals parallel to axis of red-plate compensator||Yellow||Blue|
Pearl: For the crystal color, use the mnemonic ABC (alignment, blue, calcium). If the crystal aligned with the red-plate compensator is blue, it is CPPD. Urate crystals are the opposite, being yellow when parallel to the compensator. Crystals within WBCs are more indicative of a crystalline arthropathy than free-floating crystals. Note that hydroxyapatite crystals are too small to see with polarized light