[Search for crystals in synovial fluid].

Synovial fluid analysis is a very important diagnostic procedure in rheumatology. Cell count allows the differentiation ting between inflammatory arthritis, in which cell count exceeds 2000 cells/mm3, and non inflammatory arthropathy, in which cell count is less than 1000 cells/mm3. Demonstration of crystals in synovial fluid is a rapid and inexpensive way to diagnose microcrystalline arthritis. Synovial fluid must be examined under normal and polarized light. Monosodium urate crystals are negatively birefringent, whereas calcium pyrophosphate dihydrate crystals are positively birefringent. Other crystals (cholesterol, oxalate, corticosteroids....) can also be identified in synovial fluid. Various artefacts must be avoided including anticoagulant crystals and synovial fluid must be anticoagulated with sodium heparin or citrate.