Evaluation of SIGLEC1 in the diagnosis of suspected systemic lupus erythematosus

Objectives: To evaluate and compare the diagnostic accuracy of SIGLEC1, a surrogate marker of type I IFN, with established biomarkers in an inception cohort of systemic lupus erythematosus (SLE).

Methods: SIGLEC1 was analysed by flow cytometry in 232 patients referred to our institution with suspected SLE between October 2015 and September 2020.

Results: SLE was confirmed in 76 of 232 patients (32.8 %) according to the 2019 EULAR/ACR classification criteria and their SIGLEC1 values were significantly higher compared with patients without SLE (P <0.0001). A sensitivity of 98.7 %, a specificity of 82.1 %, a negative predictive value (NPV) of 99.2 % and a positive predictive value (PPV) of 72.8 % were calculated for SIGLEC1. Adjusted to the highest reported prevalence of SLE, the NPV and PPV were >99.9 % and 0.1 %, respectively. Using receiver operating characteristic (ROC) analysis and DeLong testing, the area under the curve (AUC) for SIGLEC1 (AUC = 0.95) was significantly higher than for ANA (AUC = 0.88, P = 0.031), C3 (AUC = 0.83, P = 0.001) and C4 (AUC = 0.83, P = 0.002) but not for anti-dsDNA antibodies (AUC = 0.90, P = 0.163).

Conclusion: IFN-I pathway activation is detectable in almost all newly diagnosed SLE patients. Thus, a negative test result for SIGLEC1 is powerful to exclude SLE in suspected cases.