How to keep a wet preparation of synovial fluid

Identification of crystals in the synovial fluid (SF) is mandatory for the diagnosis of a microcrystal deposition arthropathy. In some cases, this analysis can be troublesome, especially in medical centers where a qualified practitioner is not continually present. Therefore, we investigated a method for preservation of a wet preparation of SF for 24 hours at room temperature. The procedure consisted in storing the preparation in a closed Petri plate whose bottom was covered by a cellulose compress moistened with saline (0.9% sodium chloride) separated from the slide by 2 wooden or glass sticks. The joint aspirates of 20 consecutive patients with various microcrystal arthropathies were read immediately after aspiration and reviewed after 24 hours on the slides stored according to the previously mentioned procedure. For 11 of the 20 cases, a second SF preparation was stored in normal conditions. The amounts of crystals were estimated semiquantitatively.Preparations stored in the Petri plates were clearly readable after 24 hours and crystals still identifiable on each slide. The amounts of crystals were still the same. After 24 hours, the preparations stored in normal conditions were dry, the shapes of the crystals were blurred, their amount was reduced, and birefringent artifacts were seen. In conclusion, when the amounts of SF are small and a skilled technician or a rheumatologist is not immediately available for reading the preparation, storing the wet preparation of SF in a moistened Petri plate can prove useful.