This test involves analyzing synovial fluid, the lubricating fluid found in joints, to detect the presence of crystals that can cause joint inflammation. The most common crystals include:

• Monosodium urate crystals – seen in gout
• Calcium pyrophosphate dihydrate (CPPD) crystals – seen in pseudogout. Detection is typically done using polarized light microscopy, which helps identify the shape, size, and birefringence of the crystals. The presence of crystals confirms a crystal-induced arthritis, guides treatment, and helps distinguish these conditions from infections or autoimmune joint disorders.