Sensitivity of classification criteria from time of diagnosis in an incident systemic lupus erythematosus cohort: a population-based study from Norway

Abstract

Objectives: To compare the sensitivity of 2019 European Alliance of Associations for Rheumatology/American College of Rheumatology (EULAR/ACR) classification criteria against 1997 ACR criteria for systemic lupus erythematosus (SLE), for incident SLE cases in the presumably complete population-based Nor-SLE cohort from Southeast Norway (2.9 million inhabitants).

Methods: All cases International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) coded as SLE during 2000-2017 were individually reviewed. Those with a confirmed SLE diagnosis by expert clinical assessment were included in the Nor-SLE cohort. Core clinical data were recorded, and the cases were classified according to 2019 EULAR/ACR and 1997 ACR criteria. Juvenile SLE was defined as <16 years at diagnosis and adult SLE was defined as ≥16 years at diagnosis.

Results: We included 737 incident SLE cases (701 adults, 36 juveniles). At diagnosis, 2019 EULAR/ACR criteria were more sensitive than 1997 ACR criteria for adults (91.6% vs 77.3%; p<0.001), but not for juveniles (97.2% vs 88.9%). The 2019 EULAR/ACR counts at diagnosis differed by age group and ethnicity, being higher in young cases and those originating from Asia. From time of diagnosis to study end the fulfilment rate of 2019 EULAR/ACR criteria for the adult cohort increased from 92.5% and 86.5% to 94.6% and 91.0%, respectively, for females and males (mean disease duration of 7.5 years).

Conclusion: Showing 92% criteria fulfilment already at time of SLE diagnosis by 2019 EULAR/ACR criteria versus 77% by 1997 ACR criteria, the results from this population-based study suggest that the 2019 EULAR/ACR criteria will achieve its goal of capturing more early-SLE cases for clinical trials.

Keywords: classification; epidemiology; lupus erythematosus, systemic; sensitivity and specificity.

Figure 1. Flow chart for the incident Southeast Norway SLE cohort during 2000–2017 at time of diagnosis, showing SLE case definitions and distribution of cases meeting the 1997 ACR classification criteria for SLE (1997 ACR criteria) and the 2019 EULAR/ACR classification criteria for SLE (2019 EULAR/ACR criteria), respectively. ACR, American College of Rheumatology; EULAR, European Alliance of Associations for Rheumatology; SLE, systemic lupus erythematosus.

Figure 2. For the incident Southeast Norway SLE cohort during 2000–2017, at time of diagnosis: (A) Distribution of age and sex for cases with a confirmed diagnosis. (B) Estimated percentage of cases with a confirmed SLE diagnosis fulfilling the 2019 EULAR/ACR classification criteria for SLE and the 1997 ACR classification criteria for SLE. (C) Mean and actual number of classification points for all cases fulfilling the 2019 EULAR/ACR classification criteria. (D) Calculated number of classification points for the ANA-positive and ANA-negative subsets of SLE cases not classifiable via the 2019 EULAR/ACR criteria. ACR, American College of Rheumatology; ANA, antinuclear antibodies; EULAR, European Alliance of Associations for Rheumatology; SLE, systemic lupus erythematosus.