OBJECTIVE: In a longitudinal cohort study, we investigated whether clinical and serological manifestations at the time of classification of systemic lupus erythematosus (SLE) were predictive of subsequent development of incident proteinuria as a biomarker of incident lupus nephritis.

METHODS: Patients fulfilling SLE classification criteria but having no proteinuria prior to or at the time of classification were included. Data on SLE manifestations, vital status, criteria-related autoantibodies, and SLE-associated medications were collected during clinical visits and supplemented by chart review. HR were calculated by Cox regression analyses.

RESULTS: Out of 850 patients with SLE, 604 had not developed proteinuria at the time of SLE classification. Of these 604 patients, 184 (30%) developed incident proteinuria following SLE classification. The patients had a median followup of 11 years and 7 months. Younger age and history of psychosis at the time of classification were associated with development of incident proteinuria, just as were lymphopenia (HR 1.49, 95% CI 1.08-2.06), anti-dsDNA (HR 1.38, 95% CI 1.01-1.87), and a high number of autoantibodies (HR 1.26, 95% CI 1.06-1.48).

CONCLUSION: The risk of incident proteinuria after onset of SLE was increased by the presence of lymphopenia, anti-dsDNA antibodies, psychosis, younger age, and a high number of autoantibodies at onset.