RESUMEN
The review presents modern data concerning characteristics of drawing of synovial fluid and also informativeness of its particular indices for resolving main clinical differential diagnostic task namely - selection group of septic and micro-crystal arthritis. It is demonstrated that minimal generally available span of analysis of synovial fluid is to include: finding number of leukocytes (threshold level for diagnostic of septic arthritis is 50 000 - 100 000 kl/mkl) and percentage of ploymorpho-nuclear cells (threshold level is 90%); analysis of content of crystals, Gram's stain and culture analysis of synovial fluid using light microscopy; and all this with mandatory registration of clinical data. The common evaluation of content of glucose and protein in synovialfluid is not enough informative. The detection of concentration of procalcitonin and lactate in synovial fluid is perspective for establishing septic genesis of arthritis. The sensitivity and specificity of light microscopy are quite high. Because of it absence of polarized microscope is no obstacle for implementation of crystallographic analysis of synovial fluid.