Long-term outcomes of lupus nephritis with low-level proteinuria: a multicentre, retrospective study

Objectives Reportedly, patients with LN and low-level proteinuria have favourable short-term renal outcomes. We aimed to clarify the long-term renal outcomes and overall survival of these patients, and the significance of renal biopsy in the early phase with low-level proteinuria.Methods We included 144 Japanese patients with biopsy-proven LN from 10 hospitals. Low-level proteinuria was defined by a urine protein:creatinine ratio (UPCR) of <= 1 g/gCr based on previous reports. The outcomes were end-stage renal disease (ESRD) and death.Results Compared with patients with high-level proteinuria (UPCR >1 g/gCr), those with low-level proteinuria [n = 67 (46.5%)] had significantly improved renal function at the time of renal biopsy, and low activity index and chronicity index while the frequency of class III/IV was similar (79.1% vs 84.4%, P = 0.409). In patients with low-level proteinuria, CYC usage was less, and the incidences of ESRD (3.0% vs 13.0%, P = 0.036) and death (3.0% vs 16.9%, P = 0.006) during the total observation period (median, 72 months) were low. Kaplan-Meier analysis showed significant differences in the incidence of ESRD and death between the groups. Multivariate Cox regression analysis revealed that the significant risk factors for ESRD were high chronicity index and hypertension, whereas those for death were increased age and high-level proteinuria.Conclusion Patients with LN and low-level proteinuria had favourable long-term renal and life outcomes. As these patients have substantial active pathological lesions, renal biopsy in the early phase with low-level proteinuria could enable early diagnosis and treatment and thus improve prognosis.