Urine soluble triggering receptor expressed on myeloid cells-1 is a novel biomarker for active lupus nephritis: a case-control study.

To determine the value of plasma and urine sTREM-1 levels as a biomarker of lupus nephritis (LN) as well as extra-renal systemic lupus erythematosus (SLE). Consecutive adult patients with SLE attending a tertiary lupus clinic in 2016-2018 were prospectively divided into 3 groups according to SLEDAI-2K and renal-SLEDAI scores: active renal lupus (ARL), active non-renal lupus (ANL), and inactive lupus (IL). Blood and spot urine samples from each group and matched healthy subjects were analysed by means of ELISA for plasma and urine sTREM-1 levels. The cohort included 59 patients (mean age 41.5+2.9 years, 85% female) with SLE: 15 ARL, 14 ANL, and 30 IL. The ARL group had higher scores on the SLEDAI-2K and renal-SLEDAI, and higher urine protein/creatinine ratio than the other patient groups (p=0.0001 for all). Plasma sTREM-1 level was highest in the ANL group (p=0.0085). Urine sTREM-1 level was higher in the whole SLE cohort than the healthy controls (p=0.0249), and higher in the ARL group than the others (p=0.0044). Neither plasma nor urine sTREM-1 level was associated with non-renal SLE features. On Spearman correlation analysis, urine sTREM-1 level, but not plasma sTREM-1 level, was correlated positively with renal-SLEDAI score (r=0.34, p=0.018), inversely with serum C3 and C4 levels (r=-0.42, p=0.0027 and r=-0.28, p=0.056, respectively), and positively with proteinuria (UPCR: r=0.32, p=0.0305). Urine sTREM-1 might serve as a potential biomarker of active renal SLE.