Urinary angiotensinogen: an indicator of active antineutrophil cytoplasmic antibody-associated glomerulonephritis

BACKGROUND:One of the major challenges in improving the management of antineutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA-GN) is the lack of a disease-specific indicator for histological lesions and disease activity. Here we tested the utility of urinary angiotensinogen (UAGT) as a biomarker of renal disease activity in ANCA-GN. METHODS:A prospective, two-stage cohort study was performed in ANCA-GN patients. In Stage I, UAGT was measured at the time of renal biopsy in 69 patients from two centers (test set) and 25 patients from two other centers (validation set). In Stage II, UAGT was monitored in 50 subjects in the test set for 24 months. RESULTS:In Stage I, UAGT significantly increased in ANCA-GN patients, correlating well with cellular crescents formation and active interstitial inflammation. Patients with crescentic ANCA-GN exhibited the highest UAGT compared with other histopathological classes of ANCA-GN. After multivariable adjustment, the highest quartile of UAGT, compared with the lowest quartile, associated with a 6-fold increased risk of crescentic ANCA-GN. For predicting crescentic ANCA-GN, UAGT [area under the receiver operating characteristics curve (AUC) = 0.88] outperformed albuminuria (AUC = 0.73) and estimated glomerular filtration rate (AUC = 0.69). UAGT improved the performance of those clinical markers in diagnosing crescentic ANCA-GN (P < 0.034), suggesting a role of UAGT in identifying active crescentic ANCA-GN. In Stage II, UAGT decreased after immunotherapy and increased at the time of renal relapse during the 2-year follow-up, suggesting the usefulness of UAGT to monitor disease activity over time. CONCLUSIONS:These results suggest the potential use of UAGT for assessing disease activity and renal relapse in ANCA-GN.