Persistent low complement levels and increased interferon gene expression are predictive for disease progression in patients with incomplete systemic lupus erythematosus.

•In this longitudinal study 18% of patients with incomplete Systemic Lupus Erythematosus developed classified disease in median 36months follow-up.•IFN-type I gene expression is a risk factor for progression to Systemic Lupus Erythematosus or primary Sjögren's Syndrome.•This study demonstrates that persistent low levels of complement 3 and complement 4 are associated with progression to classified disease.