A method for counting monosodium urate crystals in synovial fluid

• Main Authors: P. Montagna, R. Brizzolara, C. Ferrone, M. Cutolo, S. Paolino, M.A. Cimmino
• Format: Article
• Language: English
• Published: PAGEPress Publications 2015-06-01
• Series: Reumatismo
• Subjects: Gout, Monosodium urate crystals, Synovial fluid, Polarized microscopy.
• Online Access: http://www.reumatismo.org/index.php/reuma/article/view/827
• ISSN: 0048-7449; 2240-2683

This study was aimed to standardize the technique for counting monosodium urate (MSU) crystals in the synovial fluid (SF) of patients with gout. A total of 52 SF specimens were examined under a polarized light microscope. The amount of SF ranged between 0.1 and 45 mL (median 3 mL). MSU crystals were counted in four areas with the same size at 400x magnification. Cytological examination of the same specimens was also performed. Median leukocyte count was 400 cells/mm³ (range 50-14,000 cells/mm³), with a median percentage of polymorphonuclear leukocytes of 9% (range 0%-98%). Median crystal count was 179.5 (range 3-1600). Inter- reader and intra-reader agreement in crystal counting were good with a weighed k of 0.89 [95% confidence interval (CI) 0.85-0.94] and 0.89 (95% CI 0.84-0.93), respectively. Our data indicate that the SF MSU crystal count is a feasible and highly reliable technique.