Synovial Fluid Crystal Analysis

A mandatory microscopic examination of synovial fluid is performed under a polarized light microscope. This examination aims to detect intracellular (in phagocytic) or extracellular crystals and to identify their type based on their optical properties under polarized light: crystal morphology (acidic, rhomboid), refractive index (positive or negative), and birefringence. The main types are monosodium urate (MSU) crystals, which cause gout, and calcium pyrophosphate dihydrate (CPPD) crystals, which cause pseudogout.