The search for crystals in the synovial fluid must be carried out promptly and is very helpful in the diagnosis of microcrystalline arthropathy. If at light microscopy the fluid is negative for crystals and negative or weakly positive for alizarin red, and if the diagnosis is nevertheless suspected, analysis of the centrifuged fluid sediment facilitates the identification of crystals and increases the specificity of alizarin red (the specific stain for crystals) in the identification of apatite crystal deposits. Electronmicroscopy can the be used to confirm the presence or absence of crystals.