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

Abstract

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.

Clinical implications of synovial fluid specimen handling for crystal associated arthritides: A systematic review

“…Of the 7 studies that examined MSU detection at 24 hours compared to immediate assessment, 4 found no change 19,24,28,30 . In 1 study the detection was 100% in EDTA tubes but dropped to 92% in heparin tubes 27 .…”

“…Two studies looked at storage over several weeks. One study found 100% stability for up to 12 months but this was on samples that had been air dried and mounted on slides, and not on standard specimens 30 . In the other study that used preservative free vials, at 24 weeks, MSU was detected in 87%, 69% and 89% in the −20, 4 and 20°C group respectively 33 …”

“…Two studies utilized only polarized microscopy 26,27 . In 6 studies, the method of polarized microscopy could not be determined 28‐33 …”

The added value of synovial fluid centrifugation for monosodium urate and calcium pyrophosphate crystal detection

“…Based on the limited available evidence, EDTA preservation for several days seems comparable with instantaneous performed polarized light microscopy [14,16,17]. Thirdly, we used a conventional laboratory centrifuge, in contrast to other studies which used cytocentrifuges [6,7,9,10,[23][24][25][26]. Besides some disadvantages, mentioned before, the latter has important advantages: sedimentable particles from liquid suspensions can be directly transferred as a concentrated thin layer of cells onto a microscope slide without additional manual pipetting and it places cells and crystals in the same optical plane [6,7,9].…”

“…We already have shown that all samples that were MSU and CPP positive before centrifugation were also positive after. The centrifugation settings we used were chosen to increase comparability to other studies [6,7,9,10,[24][25][26].…”