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A method for counting monosodium urate crystals in synovial fluid
P Montagna1, R Brizzolara, C Ferrone
1Research Laboratory and Academic Division of Clinical Rheumatology, Department of Internal Medicine, University of Genova. paola.montagna@unige.it.
Abstract:
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.
Insights
Counting monosodium urate (MSU) crystals in synovial fluid (SF) is a reliable gout diagnostic method. This study standardized the SF MSU crystal counting technique, showing high inter-reader and intra-reader agreement.
Area of Science:
- Rheumatology
- Crystallography
- Medical Diagnostics
Background:
- Gout diagnosis relies on identifying monosodium urate (MSU) crystals.
- Standardized methods for counting MSU crystals in synovial fluid (SF) are needed for accurate gout assessment.
Purpose of the Study:
- To standardize a technique for quantifying MSU crystals in SF.
- To evaluate the reliability of SF MSU crystal counting.
Main Methods:
- 52 SF specimens from gout patients were analyzed.
- MSU crystals were counted under polarized light microscopy at 400x magnification.
- Leukocyte counts and polymorphonuclear leukocyte percentages were also determined.
Main Results:
- The SF MSU crystal count demonstrated good inter-reader and intra-reader agreement (weighted k = 0.89 for both).
- Median MSU crystal count was 179.5 crystals/mL.
- Leukocyte counts varied significantly, with a median of 400 cells/mm3.
Conclusions:
- SF MSU crystal counting is a feasible and highly reliable diagnostic technique for gout.
- Standardization enhances the consistency and accuracy of MSU crystal quantification in clinical practice.
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