Low hemoglobin levels are associated with Bowman’s capsule rupture and peritubular capillaritis in ANCA-associated renal vasculitis: a link of vascular injury to anemia?

Background Anemia in anti-neutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis is a severe complication that predicts renal survival. We here conducted correlative analyses to evaluate correlations of low hemoglobin levels and histopathological characteristics in ANCA-associated renal vasculitis. Methods Fifty-two patients with biopsy-proven ANCA-associated renal vasculitis observed between 2015 and 2020 were retrospectively evaluated. Spearman’s correlation was performed to assess correlations, and statistical evaluation was performed by simple and stepwise multivariable regression. Results Regarding laboratory anemia parameters, no significant association with serum hemoglobin levels was observed. Serum hemoglobin levels were associated with the estimated glomerular filtration rate in the total cohort ( β = 0.539, p < 0.001), and in the MPO-ANCA subgroup ( β = 0.679, p = 0.008). Among tubulointerstitial lesions, decreased serum hemoglobin levels correlated with peritubular capillaritis in the whole cohort ( β = − 0.358, p = 0.013), and was suggested in the MPO-ANCA subgroup ( p = 0.029, r = − 0.446). Regarding glomerular lesions, the prevalence of necrotic glomeruli significantly associated with low serum hemoglobin levels in PR3-ANCA ( β = − 0.424, p = 0.028). In the total cohort, a significant correlation between decreased serum hemoglobin levels and the occurrence of diffuse Bowman’s capsule rupture was identified ( β = − 0.374, p = 0.014), which was implied in the MPO-ANCA subgroup ( p = 0.013, r = − 0.546; p = 0.0288, slope = − 16.65). Conclusion Peritubular capillaritis and Bowman’s capsule rupture correlate with low hemoglobin levels; this may indicate that histopathological lesions are linked with inflammatory vascular injury and relative erythropoietin deficiency in ANCA-associated renal vasculitis. Graphical abstract