Abstract
INTRODUCTION: The aim of this study was to evaluate the prognostic value of the Mayo Clinic Chronicity Score (MCCS) compared with the National Institutes of Health (NIH) Chronicity Index (NIH-CI) in lupus nephritis (LN). METHODS: We conducted a retrospective cohort study of 307 patients with biopsy-proven LN evaluated at Mayo Clinic (1992-2023). Chronic histologic injury was graded using the NIH-CI and MCCS. Outcomes were proteinuria remission < 500 mg/d (PR500), complete renal response (CRR), end-stage kidney disease (ESKD), and all-cause mortality. Sex-stratified, age-adjusted Cox models were used. Prognostic performance was evaluated using change in Harrell's C-index (ΔC over a clinical model) and decision-curve analysis was used to assess clinical utility for 5-year ESKD. Subgroup analyses were used to test for effect modification by baseline estimated glomerular filtration rate (eGFR) (< 60 vs. ≥ 60 ml/min per 1.73 m(2)) and histologic class (proliferative vs. nonproliferative). RESULTS: Higher NIH-CI and MCCS scores were associated with lower likelihood of PR500 and CRR (hazard ratio [HR]: 0.75 for both) and greater risk of ESKD (HR: 1.40 for NIH-CI; 1.33 for MCCS). Adding either score to a clinical model improved discrimination for PR500 (C-index: 0.65 to 0.71), CRR (0.64 to 0.71), and ESKD (0.81 to 0.85), but not mortality (ΔC = 0.00). Decision-curve analysis showed similar net benefits for NIH-CI and MCCS. Interstitial fibrosis (IF) and tubular atrophy (TA) (IF/TA) were the only components independently predictive of renal outcomes. Our findings support applicability of both scores in nonproliferative LN and in patients with reduced baseline kidney function. CONCLUSION: The MCCS and NIH-CI provide comparable and additive prognostic information in LN. MCCS captured the chronic lesions most strongly associated with renal outcomes, with IF/TA as the principal determinant of prognosis.