痛风病人关节液检测可见尿酸盐结晶，如图示呈针状。如果用红光补偿棱镜在偏振光下观察，在补偿棱镜的主（“慢”）轴方向呈黄色（反双折射）而在相反的垂直方向呈蓝色。
痛风性关节炎：大拇趾肉眼 X线 软组织内痛风石(低倍镜) 关节液查见尿酸盐结晶
If synovial fluid is aspirated from a patient with gout, the fluid can be examined for the presence of sodium urate crystals, which are seen here to be needle shaped. If they are observed under polarized light with a red compensator, they appear yellow (negatively birefringent) in the main ("slow") axis of the compensator and blue in the opposite perpendicular direction.