Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with a broad spectrum of clinical and immunological manifestations, that is difficult to diagnose. The classification criteria for SLE are essential for standardization of cohorts and reproducibility of clinical trials.1

In 2019, the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR) drew up new classification criteria for SLE2 (EULAR/ACR-2019). These were more sensitive and specific than the 1997 criteria of the ACR (ACR-1997) and the 2012 criteria of the Systemic Lupus International Collaborating Clinics (SLICC-2012). The methodology included an initial phase comprising a systematic review of the literature,3 a Delphi exercise with 145 international experts,4 a cohort of 616 patients with recent-onset SLE, and a survey of 339 individuals with SLE. In the second phase, 19 experts used the nominal group technique to reduce the number of classification criteria to 21.5 In the third phase, the criteria were separated into clinical and immunological criteria. Weighting was based on a representative sample of patients with SLE, and pairs of criteria were compared using a multicriteria decision analysis. The last phase, of refinement and validation of the criteria, was based on a validation cohort comprising 1270 individuals (696 patients with SLE and 574 controls with diseases mimicking SLE). The sensitivity and specificity of the new criteria were 96.1% and 93.4%, respectively, which represents an improvement on the ACR-1997 and SLICC-2012 criteria,2 thus enabling greater accuracy and a lower percentage of false positives and negatives.

The most relevant modification introduced by EULAR/ACR-2019 is the presence of antinuclear antibodies (ANA) at titers of ≥1/80 (measured as HEp-2 cells or equivalent) as an essential criterion, thus excluding patients with persistently negative ANA titers. This criterion is based on the results of a systematic review of 13 080 patients with SLE, in which an ANA titer ≥1/80 had 97.8% sensitivity.3

In addition, the clinical and immunological criteria were redesigned and are now subdivided into 7 clinical domains (constitutional, hematologic, neuropsychiatric, serosal, mucocutaneous, musculoskeletal, and renal) and 3 immunological domains (antiphospholipid antibodies, low complement levels, and SLE-specific antibody). Unexplained fever was included as a constitutional clinical criterion. Within each domain, the criteria are weighted with values ranging from 2 to 10 according to their relative weight in the diagnosis of SLE based on available scientific evidence. Therefore, based on the new criteria, diagnosis of SLE requires a positive ANA titer ≥1/80, a clinical criterion, and a score ≥10. The changes in weighting make it possible to classify as having SLE patients with class 3–4 lupus nephritis as the only clinical manifestation and a positive ANA titer. As for mucocutaneous criteria, even if a patient presents with various cutaneous manifestations that are typical of SLE, only that with the highest value will be scored (Table 1). Therefore, in line with the new classification, it is not possible to classify an SLE patient based only on mucocutaneous findings.

The new EULAR/ACR-2019 classification criteria for SLE are more sensitive and specific and include major modifications: positive ANA titers as an essential requirement, new clinical criteria, and changes in weighting. These are aimed at standardizing SLE cohorts and including individuals with a shorter disease course.