Serum calcification propensity is independently associated with disease activity in systemic lupus erythematosus

BACKGROUND: Systemic lupus erythematosus (SLE) is associated with severe cardiovascular complications. The T(50) score is a novel functional blood test quantifying calcification propensity in serum. High calcification propensity (or low T(50)) is a strong and independent determinant of all-cause mortality in various patient populations. METHODS: A total of 168 patients with ≥ 4 American College of Rheumatology (ACR) diagnostic criteria from the Swiss Systemic lupus erythematosus Cohort Study (SSCS) were included in this analysis. Serum calcification propensity was assessed using time-resolved nephelometry. RESULTS: The cohort mainly consisted of female (85%), middle-aged (43±14 years) Caucasians (77%). The major determinants of T(50) levels included hemoglobin, serum creatinine and serum protein levels explaining 43% of the variation at baseline. Integrating disease activity (SELENA-SLEDAI) into this multivariate model revealed a significant association between disease activity and T(50) levels. In a subgroup analysis considering only patients with active disease (SELENA-SLEDAI score ≥4) we found a negative association between T(50) and SELENA-SLEDAI score at baseline (Spearman’s rho -0.233, P = 0.02). CONCLUSIONS: Disease activity and T(50) are closely associated. Moreover, T(50) levels identify a subgroup of SLE patients with ongoing systemic inflammation as mirrored by increased disease activity. T(50) could be a promising biomarker reflecting SLE disease activity and might offer an earlier detection tool for high-risk patients.