What is the best way to diagnose gout? How are gout crystals recognized on polarized microscopy? How are pseudogout crystals recognized on polarized microscopy?
Gout is best diagnosed by visualization of crystals in a joint aspirate. Gout (monosodium urate) crystals have a needle-shaped appearance under light microscopy. Under a polarizing light microscope, these needle-shaped crystals are strongly negatively birefringent. This means that when the compensator portion of the microscope is positioned parallel to the long axis of the crystal, the crystal appears bright yellow. When the compensator is turned perpendicular to the crystal, the crystal appears bright blue.
Pseudogout (or calcium pyrophosphate) crystals are rhomboid-shaped and weakly positively birefringent. This means that when the compensator is parallel to the long axis of a pseudogout crystal, the crystal has a faint blue colour. When the compensator is perpendicular to the crystal, the crystal is faintly yellow.
