Low-level proteinuria at the initial diagnosis of systemic lupus erythematosus significantly increases the risk of developing proteinuria-predominant lupus nephritis

Purpose A proportion of patients with systemic lupus erythematosus (SLE) present with subclinical low-level proteinuria at initial diagnosis that does not meet the formal classification criteria for lupus nephritis (LN). This study aimed to investigate the association between low-level proteinuria at SLE onset and the risk of developing proteinuria-predominant LN. Patients and methods This was a retrospective cohort study using medical records of patients newly diagnosed with SLE from Fujian Medical University Union Hospital between December and March. Inclusion required urine dipstick proteinuria ≤2+; if quantified, protein excretion <500 mg/24h (by the urine protein-to-creatinine ratio [UPCR] or 24-hour proteinuria). Demographic, clinical, and laboratory data were collected at the time of initial diagnosis, as well as urinalysis, urine sediment, UPCR, and 24-hour proteinuria during follow-up, where available. The association between various baseline variables and the subsequent development of proteinuria-predominant LN was analyzed using a Cox proportional hazards model. Results Of 330 patients screened, 297 were eligible for inclusion in the final analysis, of whom 85 patients had low-level proteinuria at the initial diagnosis. According to multivariable-adjusted models, low-level proteinuria significantly increased the risk of proteinuria-predominant LN ( P < 0.001, hazard ratio[HR] = 3.355, 95% confidence interval [CI]: 1.6646.765), as did male sex ( P = 0.001, HR = 3.178, 95% CI: 1.563–6.460). Conclusion This study highlights that SLE patients with low-level proteinuria at initial diagnosis may require enhanced monitoring for LN, enabling early detection. Future studies are needed to determine the necessity of early intervention.