Can we predict kidney involvement in patients with systemic lupus erythematosus? A retrospective cohort study with independent validation.

OBJECTIVES:To discern predictive factors for incident kidney involvement in patients with systemic lupus erythematosus (SLE). METHODS:Patients with SLE from the 'Attikon' Lupus cohort were monitored for lupus nephritis (LN), defined by kidney histology and/or classification criteria. Demographic and clinical characteristics at baseline were compared against patients who did not develop LN. LN-free survival curves were generated by Kaplan-Meier. A multivariate Cox proportional hazards model was used to identify independent predictors of LN. Independent validation was performed in the University of Crete Lupus registry. RESULTS:Among the 570 patients in the derivation cohort, 59 exhibited LN as their initial presentation, while an additional 66 developed LN during the follow-up period (collectively, 21.9% incidence). In the latter group, baseline factors predictive of subsequent kidney involvement were male sex (multivariable-adjusted [a]HR 4.31, 95% CI: 1.82-10.2), age of SLE diagnosis below 26 years (aHR 3.71, 95% CI: 1.84-7.48), high anti-dsDNA titre (aHR 2.48, 95% CI: 1.03-5.97) and low C3 and/or C4 (although not statistically significant, aHR 2.24, 95% CI: 0.83-6.05, p= 0.11). A combination of these factors at time of diagnosis conferred an almost 90-fold risk compared with serologically inactive, older, female patients (aHR 88.77, 95% CI : 18.75-420.41), signifying a very high-risk group. Independent validation in the Crete Lupus registry showed concordant results with the original cohort. CONCLUSION:Male sex, younger age and serologic activity at SLE diagnosis are strongly associated with subsequent kidney involvement. Vigilant surveillance and consideration of early use of disease-modifying drugs is warranted in these subsets of patients.