Monitoring disease activity in systemic lupus erythematosus with single-molecule array digital ELISA quantification of serum interferon-α

IF 7.873International audienceObjectivesNo simple or standardized assay is available to quantify interferon‐α (IFNα) in routine clinical practice. Single‐molecule–array (Simoa) digital enzyme‐linked immunosorbent assay (ELISA) technology enables direct IFNα quantification at fg/mL concentrations. This study was undertaken to assess IFNα digital ELISA diagnostic performances to monitor systemic lupus erythematosus (SLE) activity.MethodsIFNα concentrations in serum samples from 150 consecutive SLE patients in a cross‐sectional study were determined with digital ELISA and a functional biological activity assay (bioassay). According to their SELENA–SLEDAI flare composite, patients were divided into groups with inactive (SLEDAI 0), and into groups with no flare or mild/moderate flare or severe flare.ResultsBased on healthy blood donors, the abnormal serum‐IFNα level threshold value was 136 fg/mL. Next, using receiver operating characteristics curves for an SLE‐patient series, widely heterogeneous for disease activity and organ involvement, the threshold IFNα value associated with active disease was determined to be 266 fg/mL. The digital ELISA‐assessed serum‐IFNα level was a better biomarker of disease activity than the Farr test: its specificity, likelihood ratio for positive results and positive‐predictive value better discerned active SLE or flare from inactive patients. The digital ELISA was more sensitive than the bioassay to detect low‐abnormal serum‐IFNα concentrations and patients with low disease activity.ConclusionDirect serum‐IFNα determination with a highly sensitive assay might improve monitoring of clinical SLE activity and selection of the best candidates for anti‐IFNα treatment