Dried cytospin preparations of synovial fluid are a stable material for long-time storage and delayed crystal analysis.

The aim of this study was to evaluate dried SF cytospin preparations as a suitable medium for long-time storage and delayed crystal analysis. For this purpose, we analyzed ten MSU-positive, ten CPPD-positive and 20 crystal-negative SF at baseline (wet preparation), after 24 h, 1 week, 4 weeks, 6 months and 12 months for the occurrence of crystals. After cytocentrifugation for 10 min at 700 rpm in a Shandon Cytospin 4 cytocentrifuge (Thermo Fisher Scientific, Waltham, USA), the sediments were dried on the slides and examined in blinded fashion at any time point by an experienced analyst using polarized microscopy. The crystal content of the initially MSU- and CPPD-positive samples was positively confirmed at any time point of the study, whereas the controls remained crystal-negative during the whole study period. Thus, compared to the examined wet preparations at baseline, there were no false positive or false negative results observed. In conclusion, dried cytospin preparations were confirmed as a suitable material for long-time storage and delayed crystal identification.