Impact of disease duration and gender on the sensitivity and specificity of 2015 ACR/EULAR classification criteria for gout. Cross-sectional results from an Italian multicentric study on the management of crystal-induced arthritis (ATTACk).

Objectives: We aimed to assess the performance of the 2015 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) gout classification criteria in an Italian cohort of patients with crystal-induced arthritis stratified by disease duration and gender in a real-life setting.

Methods: Consecutive patients referred to Rheumatology Units for suspected acute crystal-induced arthritis were enrolled in a multicentre cohort study by the Italian Society of Rheumatology which was designed to improve the management of crystal-induced arthritis (ATTACk). To test the performance of the criteria (sensitivity and specificity), the presence of monosodium urate (MSU) crystals in synovial fluid (SF) was used as gold standard. Subgroup analyses by gender and disease duration were performed.

Results: Two hundred and seventy-seven patients were enrolled. SF analysis was available in 137 (49%) patients. Complete SF analysis and ACR/EULAR scores were obtained in 44% of patients. MSU crystals were found in 66% of patients. The sensitivity and the specificity of all criteria sets were 78% (95%CI, 67-86) and 98% (95%CI, 87-100), respectively; only clinical criteria yielded 70% (95%CI, 59-80) sensitivity and 93% (95%CI, 80-98) specificity, respectively. In early-stage disease (<2 years), the sensitivity dropped to 58% (95%CI, 39-75), while the specificity was 100% (95%CI, 85-100).

Conclusions: The ACR/EULAR criteria showed good performance in patients presenting with acute arthritis; changes were observed when a subset of criteria were used, especially in early-stage disease.