Liquide synovial normal et pathologique

Synovial fluid analysis is a very important diagnosis step in rheumatology. Cell count allows to differenciate inflammatory arthritis, in which cell count exceeds 2000 cells/mm³, from non inflammatory arthropathy, in which cell count is less than 1000 cells/mm³. Bacteriological studies must be performed on an emergency basis before antibiotic administration, and must include direct examination and culture, which allow the diagnosis of septic arthritis to be made and the choice of antibacterials. Demonstration of crystals in synovial fluid is a rapid and unexpensive way to diagnose microcrystalline arthritis. Synovial fluid must be examined under normal and polarized light. Equipment of the polarizing light microscope with a compensator and a rotating stage increases its diagnosis performances. 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.