Significance of the weighted complement domain of the EULAR/ACR classification criteria in juvenile onset systemic lupus erythematosus

Objective We aimed to compare the clinical and laboratory characteristics of patients with SLE according to the weighted complement status of the EULAR/ACR criteria and investigate whether different weighting of the complement status at disease onset is associated with outcomes. Methods Patients diagnosed with juvenile onset SLE who fulfilled the 2019 EULAR/ACR classification criteria were retrospectively analyzed. Results Among 43 patients included, hypocomplementemia was observed in 37 (86%), mostly with a low level of both complement C3 (C3) and complement C4 (C4) (53.5%). In patients with low levels of both C3 and C4, more common cutaneous (65.2% vs 28.6%, p: 0.045), musculoskeletal involvement (78.3% vs 42.9%, p: 0.039), autoimmune hemolytic anemia (52.2% vs 14.3%, p: 0.035), positive anti-dsDNA (65.2% vs 21.4%, p: 0.017) and anti-Sm antibodies (60.9% vs 21.4%, p: 0.04) were observed. In addition these patients had higher scores from the 2019 EULAR/ACR classification criteria (26 vs 15.5, p: < 0.0001). Remission and flare rates, and SLE associated damage were not differed according to the complement status in patients with hypocomplementemia. Conclusion Observation of more frequent clinical and serological activity with higher total scores from the EULAR/ACR classification criteria supported the higher scoring of patients with low C3 and C4 in the weighted criteria. However, since significant number of patients did not exhibit low complement C4, and the frequency of kidney involvement did not differ according to the weighted complement status, complement C3 might be suggested as a more important diagnostic tool in patients with juvenile onset SLE. Also, weighted complement status at onset did not seem to affect the disease outcomes.