Urine IgM excretion predicts outcome in ANCA-associated renal vasculitis

Background. Renal function at diagnosis is a strong predictor not only of renal survival but also of patient survival of those with anti-neutrophil cytoplasmic antibody (ANCA)-associated small vessel vasculitis (ASVV). Apart from the renal function at diagnosis, there are no other established risk factors for renal outcome in ASVV. We have previously reported that in other forms of glomerular diseases, an increased urine excretion of IgM is an early marker of poor renal outcome. Methods. In this single-centre observational study, the prognostic significance of urine IgM excretion and other selected prognostic markers was studied in 83 consecutive patients (49 males, 34 females) with ASVV with renal involvement. Results. Patient survival at 1 and 5 years was 93 and 77%, respectively, and the corresponding figures for renal survival censored for death were 84 and 76%. Univariate analysis indicated that patient survival was inversely associated with age, male sex, serum creatinine, low serum albumin and high urine IgM excretion. Renal survival was inversely associated with serum creatinine, albuminuria and urine IgM. Multivariate analysis determined that only old age and high urine IgM excretion were independent predictors of patient survival [odds ratio (OR) = 11.2 and 4.4, respectively, P <0.01]. Urine excretion of IgM was the only independent predictor of end-stage renal disease (OR = 19.8, P = 0.004). Overall, 35% of the patients reached the composite end-point of either death or renal replacement therapy. Urine IgM excretion was the most potent single predictor of such an outcome (OR = 7.7, P = 0.000). Conclusion. The occurrence of an increased amount of IgM in urine at presentation is a strong marker of poor prognosis for patients with ANCA-associated renal vasculitis.