The aspirate on the bench

A synovial fluid aspirate reaches the laboratory 35 minutes after collection. The fluid arrives in three containers: a sterile, additive-free container for culture, a liquid-EDTA tube for cell count and differential, and a second additive-free container for crystal examination. The EDTA tube is short filled but not clotted. Whether the cell count can be released depends on two things: whether the fill meets the tube's validated minimum volume and whether the liquid-EDTA dilution effect has been accounted for in the validated procedure. The fluid is yellow and cloudy. Assess viscosity by how the fluid behaves when aspirated and expelled through a pipette, not by pulling a drop between your fingers, which is neither safe nor standardized.

None of that gross appearance identifies a crystal. Color and clarity are observations that narrow the differential a little; they are not a crystal call and not a diagnosis by themselves. First decide whether the specimen is suitable for count and crystal work. If it is, identify the crystal under compensated polarized light.

A request for both a cell count and a crystal search on limited fluid volume is common. The order in which aliquots are protected matters: a sterile, additive-free tube reserved for microbiology has to be preserved even when volume is tight, because once that aliquot is contaminated or consumed there is no way to recover it for culture.

Before touching a slide, confirm which aliquot is which, whether any tube shows a clot, and how much time has passed since collection, because all three change what the rest of the workup can support.