Liquide synovial normal et pathologique

Analysis of the joint fluid is an important step of the rheumatologic diagnosis. Cell count must be performed early after puncture; a cell count over 2000 elements/mm³ establishes a diagnosis of inflammatory rheumatism whereas a mechanical affection is diagnosed when it is less than 1000 elements/mm³. A bacteriological assessment should be carried out in emergency prior to any antibiotherapy. Evidence of bacterium by direct examination or culture indicates an infectious arthritis and allows selecting the adequate antibiotic treatment. Crystal screening is a rapid and inexpensive procedure for the diagnosis of crystal-related arthritis. The assessment must run on a fresh fluid sample, between two strips, using successively a standard microscope and a polarizing microscope. Adding a compensator and a revolving stage helps identifying more reliably monosodium urates, with a negative double refringency, and dehydrated calcium pyrophosphates with a positive double refringency. Other crystals (cholesterol, oxalate, cortisone…) may be identified also. To avoid artefact sources, especially anticoagulant crystals, the fluid sample must be collected on a small amount of sodium or citrate heparinate.