[Synovial fluid analysis].

At present, the study of the synovial fluid (SF) is a tool that is used frequently in specialized laboratories because it allows the establishment of diagnosis of crystal associated arthropathies, supports the diagnosis of septic arthritis and helps establish other rheumatologic diagnoses such as monoarthritis or joint effusion. The complete study of the SF includes the following analyses: 1. Macroscopic; 2. Microscopic; and 3. Specific stains. Each one provides information of the joint's state and helps in the establishment of diagnosis and treatment. The characteristics that must be described in the macroscopic analysis are: color, volume and viscosity. Microscopic analysis of the SF confirms the presence of an inflammatory or infectious processes and allows for the detection and identification of crystals. Polarized light microscope is a fundamental tool for the analysis of SF and for the identification of the crystals present in the samples, which not only depend on the form, but also of their birefringence. It is important to mention that in the microscopic analysis, artifacts can confuse the inexperienced observer. A suitable interpretation of the analysis of SF requires the observation by at least two experienced observers. The information that the analysis of SF provides to the clinicians gives them the necessary elements to establish the diagnosis and to decide on treatment. Specific stains in the analysis of SF help in the identification of non-birefringent crystals as those of calcium hydroxypatite. In SF analysis, new fields are being explored that include quantification of cytokines, chemokines, immunoglobulins and the characterization of cell lineages.