Persistence of Crystals in Stored Synovial Fluid Samples

• Published in: Journal of rheumatology 2020-09, Vol.47 (9), p.1416-1423
• Main Authors: Pastor, Sonia, Bernal, José-Antonio, Caño, Rocío, Gómez-Sabater, Silvia, Borras, Fernando, Andres, Mariano
• Format: Article
• Language: English
• ISSN: 0315-162X; 1499-2752
• DOI: 10.3899/jrheum.190468

The lack of immediate access to a polarized light microscope is often used as an argument to justify the clinical diagnosis of crystal-related arthritis. The aim of this study was to assess the influence of time since sampling and preservation methods on crystal identification in synovial fluid samples under polarized light microscopy. Prospective, longitudinal, observational factorial study, analyzing 30 synovial fluids samples: 12 with monosodium urate crystals (MSU) and 18 with calcium pyrophosphate (CPP) crystals. On extraction, each fluid sample was divided into four subsamples (120 subsamples in total). Two were stored in each type of tube-heparin or ethylenediaminetetra-acetic acid (EDTA) as preserving agents -, at varying temperatures - room temperature or refrigerated at 4°C (39.2°F). Samples were analyzed the following day (T1), at three days (T2), and at seven days (T3) by simple polarized light microscopy, and the presence of crystals was recorded. The identification of crystals in the MSU group was similar between groups, with crystals observed in 11/12 (91.7%) of room temperature samples and in 12/12 (100%) of refrigerated samples at T3. However, the identification of CPP crystals tended to decrease in all conditions, especially when preserved with EDTA and kept at room temperature (12/18 [66.7%] at T3), while less reduction was seen in refrigerated heparin-containing tubes. Preserving samples with heparin in refrigerated conditions allows a delayed microscopic examination for crystals. Avoiding crystal-proven diagnosis due to the immediate unavailability of a microscope no longer appears justified.