Concordance between fresh joint fluid analysis by the rheumatologist and joint fluid analysis at the laboratory: Prospective single-center study of 180 samples.

Objectives: To assess the diagnosis usefulness of fresh joint fluid analysis by the rheumatologist.

Methods: Prospective single-center 1-year study at a university hospital in Rennes, France. A rheumatologist determined whether the freshly collected fluid suggested a mechanical or inflammatory condition and contained monosodium urate (MSU) and/or calcium pyrophosphate (CCP) microcrystals. Agreement between the rheumatologist results and laboratory results was assessed based on the kappa coefficient (κ). We then determined the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of joint fluid analysis by the rheumatologist and by the laboratory, using the final diagnosis based on the full set of clinical, laboratory, and imaging findings as the reference standard.

Results: We included 180 joint fluid samples. The κ values were 0.80 for mechanical or inflammatory fluid, 0.97 for presence of MSU microcrystals, and 0.69 for presence of CCP microcrystals. The rheumatologist findings had 94.2% sensitivity and 84.6% specificity for inflammation; corresponding values were 80.7% and 100% for MSU microcrystals and 66.7% and 93.2% for CCP microcrystals.

Conclusion: Fresh joint fluid examination by the rheumatologist shows good to excellent agreement with the laboratory analysis for determination of the mechanical or inflammatory nature of the fluid and for detection of MSU and CCP microcrystals.