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.