There are three characteristics of synovial fluid that you can analyze clinically right away: the color of the fluid, the clarity of the fluid, and the viscosity of the fluid. None of these findings may be highly sensitive or specific to your diagnosis by themselves, but taken together with the other labs and your history and physical exam, they may contribute to your overall clinical acumen.
Color and clarity may vary. Normal synovial fluid is clear and colorless or straw-colored. Abnormal fluid may look cloudy, opaque, and/or differently colored. For example, cloudy fluid may indicate an infection, and pink or reddish fluid may indicate the presence of blood.
Red or red-tinged fluid indicates hemorrhage in the joint associated with trauma or inflammation or hemorrhage that has occurred during the collection process. Xanthochromia is a yellow-orange discoloration that indicates prior hemorrhage and hemoglobin breakdown. White or light yellow coloration or sediment indicates an increase in the nucleated cell count because of inflammation, sepsis, or neoplasia, or it may indicate crystal formation. An increase in turbidity is caused by suspended particulates, such as red blood cells, white blood cells, organisms, fibrin, neoplastic cells, or crystals. Alterations in color or turbidity caused by crystals or neoplastic cells are extremely rare.
Color
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