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Abstract
Background A standardized validated definition for gout attacks (flares) is not available. Two provisional definitions published in 2012 were based on patient-reported elements (patient-defined attack, pain at rest greater than 3 in a 0–10 numeric rating scale, presence of at least one swollen joint, presence of at least one warm joint) (1). These definitions had acceptable sensitivity and specificity but lacked external validation which is necessary before they can be adopted in gout clinical studies.
Objectives To perform external validation of previously published preliminary gout attack (flare) definitions in patients with gout.
Methods We enrolled 509 participants with gout from 17 international sites in a cross-sectional study performed during routine clinical care. All patients met the 2015 ACR/EULAR classification criteria for gout (2). Criteria for the previously published gout attack definitions were collected by a site investigator and the final adjudication of a gout attack status was done by a local expert rheumatologist, through an evaluation independent from that of the site investigator. Logistic regression, Bayesian statistics, and receiver-operator curves were used to calculate the final diagnostic performance of the gout attack definitions.
Results The mean age of participants was 57.5 years (standard deviation [SD] 13.9) and 89% were men. Mean disease duration was 12.3 (SD 10.3) years, 35% had tophi, and 75% were taking urate-lowering therapies. The previously published and favored definition requiring the presence of 3 or more out of 4 criteria (“number of criteria”) was found, using the current study data, to be 85% sensitive and 95% specific in confirming the presence of an attack in patients with gout (Table). The concurrent logistic regression model had an area under the curve of 0.97. The previously published definition based on a classification and regression tree algorithm (entry point pain at rest >3 followed by patient-defined attack “yes”) was 73% sensitive and 96% specific using the current study data (Table). The “number of criteria” approach with a cut-point at 3 or more out of 4 criteria had higher diagnostic accuracy using the current study data than in its initial 2012 description (92% versus 84%, table). (1) Finally, using current study data the “number of criteria” approach at 3 or more out of 4 criteria had higher accuracy to the classification and regression tree algorithm based approach (92% versus 89%) but with a much better sensitivity (85% versus 73%).
Conclusions The definition requiring the presence of 3 or more out of 4 patient-reported criteria is validated to be sensitive, specific, and accurate in identifying attacks (flares) in patients with gout using an independent large international sample. Having a validated gout attack definition will improve ascertainment of outcomes in gout clinical studies.
References
Gaffo AL et al. Arthritis Rheum. 2012;65:1508.
Neogi T et al. Ann Rheum Dis 2016;75:473.
References
Acknowledgements Funding provided by AstraZeneca, Ardea Biosciences, Inc., and Ironwood Pharmaceuticals.
Disclosure of Interest A. Gaffo Consultant for: SOBI, N. Dalbeth Grant/research support from: AstraZeneca, Consultant for: Takeda, Pfizer, AstraZeneca, Cymabay, and Crealta, Paid instructor for: Takeda, AstraZeneca, J. Singh Grant/research support from: Takeda, Savient, Consultant for: Savient, Takeda, Regenron, Merz, Bioiberica, Crealta, Allergan, WebMD, UBM LLC, American College of Rheumatology, K. Saag Consultant for: Takeda, Horizon, SOBI, W. Taylor Consultant for: Pfizer, AstraZeneca, Abbvie, Roche