Gout crystals under polarized light are which shape and birefringence?

• A. Needle-shaped crystals that are negatively birefringent
• B. Needle-shaped crystals that are positively birefringent
• C. Rhomboid-shaped crystals that are negatively birefringent
• D. Hexagonal crystals that are neutral birefringent

Answer: (A)

Gout crystals are monosodium urate crystals that are needle-shaped. Under polarized light, they exhibit negative birefringence, meaning they appear blue when their long axis is aligned with the slow axis of the compensator and shift toward other colors as you rotate them. This combination—needle-shaped and negatively birefringent—is the hallmark seen in gout. By contrast, crystals from pseudogout are rhomboid-shaped and positively birefringent, appearing yellow when aligned parallel to the slow axis, which helps distinguish them.