Background There is paucity of population-based studies that investigate the epidemiology of lupus nephritis (LN) and its long-term outcomes.

Methods We used the Rochester Epidemiology Project (REP) a record-linkage system that includes all residents from Olmsted County, Minnesota since 1966 with additional counties since 2010. A cohort of LN patients between 1976 and 2018 in an eight-county region was identified based on (1) biopsy proven LN in the presence of a positive ANA or ds-DNA antibody, or (2) meeting ACR/EULAR 2019 criteria and having documented proteinuria (500 mg in 24hrs urine collection or protein/creatinine ratio > 0.5) that did not have a better explanation than SLE. Age- and sex-specific incidence rates and point prevalence for four decades, adjusted to 2000 US total population, were reported. Standardized mortality ratio (SMR), survival rates, and time to end-stage renal disease (ESRD) were estimated using Kaplan-Meier methods. Poisson regression models were used to look at trends in relative survival over time.

Results There were 72 incident LN from 1976-2018. Mean age was 38.4 years (SD 16.24), 76% were female, and 69% non-Hispanic White. The overall LN incidence between 1976 and 2018 was estimated at 1 per 100,000 (95%CI 0.8-1.3). The incidence was highest in 30-39 age group. The overall incidence of LN increased from 0.7 to 1.3 with sex specific incidence in males quadrupling from 0.2 to 0.8 per 100,000 between 1976-1988 and 2000-2018 periods (table 1). LN prevalence increased from 16.8 per 100,000 in 1985 to 21.2 in 2015. LN had SMR of 6.33 (95%CI 3.81-9.89) compared to the general population. Survival was 50% at 20 years, and among survivors 40% had ESRD. There was a widening mortality gap with an increase in the SMR of 7% per year (1.07; 95%CI 1.03-1.10, p<0.001) or almost a doubling of the SMR every 10 years (1.90 per 10 years; 95%CI 1.33-2.70).

Conclusions The incidence and prevalence of LN has increased in the last 40 years. Long-term outcomes in patients with LN remain poor. Patients with LN had a mortality rate of more than 50% at 20 years and of those surviving, 40% had ESRD. The widening mortality gap we observed with near doubling of SMR each decade shows that the mortality reduction in LN patients is not keeping up with the mortality improvements of the general population despite changes in clinical practice over the decades.