Cytospin preparations are superior to common smears in the detection of monosodium urate crystals in low-cellular synovial fluids

In cases of gout with a low synovial fluid (SF) leukocyte count and atypical clinical presentation, such as in intercritical periods, the load of monosodium urate (MSU) crystals is frequently low, and thus, methods to improve the crystal detection may be beneficial. We compared the MSU crystal detection rates between cytospin slides and common smear preparations in low-cellular (<2,000/μl) SF samples of patients with gout. We determined the number of MSU crystals/15 high power fields (HPF) at × 1,000 magnification by polarised microscopy in cytospin preparations and smears in SF samples of 17 patients with MSU-crystal-proven gout and compared the two methods statistically. All of the cytospin slides (100 %) contained MSU crystals and showed a median number of 124 crystals/15 HPF (range 2–3,915), whereas 5 of the 17 smears (29 %) were MSU-crystal-negative, with a median count of 2 crystals/15 HPF (range 0–430/HPF). The difference was statistically highly significant (p < 0.0001). In conclusion, we have shown that the cytospin technique is superior to smears in the detection of MSU crystals in SF with a low SF leukocyte count. In light of our observations, we recommend the use of cytocentrifuges for routine crystal analysis in such cases.