Editing Synovial fluid (section)

=== Microscopy ===
Microscopic analysis of synovial fluid is performed to evaluate for cell count and crystals.  Crystals include [[monosodium urate crystals]], [[calcium pyrophosphate]], [[hydroxyapatite]] and [[corticosteroid]] crystals.<ref name=demais2009/>

Monosodium urate crystals are seen in [[gout]] or gouty arthritis and appear as needle-shaped negatively birefringent crystals varying in length from 2 to 20&nbsp;[[μm]]. With negative birefringence, the crystals appear yellow in parallel light and blue with perpendicular light.

[[Calcium pyrophosphate]] crystals are seen in [[pseudogout]] (also known as calcium pyrophosphate deposition disease or, CPPD). These crystals are rod-shaped or rhomboids varying in length from 2 to 20&nbsp;μm and with positive birefringence (blue with parallel light, yellow with perpendicular light).

[[Hydroxyapatite]] crystals are small and negatively birefringent. They are usually only detectable with an [[Alizarin Red S]] stain.

[[Corticosteroid]] crystals may be seen following therapeutic corticosteroid injection into the joint space. They appear blunt, jagged, and show variable birefringence.<ref name=demais2009/>