Low levels of complement factor C3 at diagnosis can predict outcome in antineutrophil antibody associated vasculitis

Comparison of clinical and laboratory data of adult patients with cutaneous IgA vasculitis and non-IgA vasculitis

BACKGROUND

Immune complex vasculitides may be subdivided into adult IgA small vessel vasculitis (aIgA-SVV; i.e. adult Henoch-Schönlein purpura) and non-IgA-SVV (hypersensitivity vasculitis, etc.).

OBJECTIVES

To evaluate the clinical and laboratory parameters of inpatients fulfilling the diagnostic criteria for aIgA-SVV and non-IgA-SVV.

METHODS

Twenty-nine adults aged ≥ 20 years with aIgA-SVV [according to the European League Against Rheumatism/Paediatric Rheumatology International Trials Organisation/Paediatric Rheumatology European Society (EULAR/PRINTO/PRES) criteria] and 53 adults with non-IgA-SVV (according to the 2012 revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides) were compared with respect to a variety of clinical and laboratory parameters by uni- and multivariable analyses.

RESULTS

Compared with patients with aIgA-SVV, the platelet-to-lymphocyte ratio was significantly higher in patients with non-IgA-SVV. Serum C3 levels and mean corpuscular haemoglobin concentration in patients with non-IgA-SVV were significantly lower compared with patients with aIgA-SVV. Proteinuria and haematuria were significantly more common in patients with aIgA SVV, and were significantly correlated with systemic immune-inflammation biomarkers only in patients with aIgA-SVV. In patients with aIgA-SVV, higher lactate dehydrogenase and C-reactive protein were strong independent predictors for the presence of proteinuria and proteinuria. In patients with non-IgA-SVV, female sex was a protective factor for proteinuria, while skin lesions on the upper extremities proved to be a significant independent predictor of haematuria.

CONCLUSIONS

We detected several clinical and laboratory differences between patients with aIgA-SVV and non-IgA-SVV. Distinct predictors for renal involvement were not observed in either group, indicating that aIgA-SVV and non-IgA-SVV are similar conditions but do not appear to represent the same entity.

Serum Uric Acid Associates with Systemic Complement C3 Activation in Severe ANCA-Associated Renal Vasculitides

Involvement of the complement system is key to the pathogenesis of antineutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis, but immunometabolic implications, especially on serum uric acid (UA) levels, still need to be elucidated. A total of 34 patients with biopsy-proven ANCA-associated renal vasculitis between 2015 and 2020 were retrospectively enrolled. Serum UA levels were correlated with clinical and histopathological characteristics, separated for critically ill (CI, n = 19), myeloperoxidase (MPO)-ANCA (n = 21) and proteinase 3 (PR3)-ANCA (n = 13) subgroups. We here identified inverse correlations of serum UA levels and complement C3 levels in the total cohort (p = 0.005) and the CI subgroup (p < 0.001). Intrarenal complement C4d deposition in venules correlated with serum UA levels in the total cohort (p = 0.007) and in the CI subgroup (p = 0.016). Significant associations of serum UA levels and tubulitis in areas of scarred cortex (t-IFTA) were identified in the total cohort (p = 0.008), and both subgroups of CI (p = 0.034) and MPO-ANCA (p = 0.029). In PR3-ANCA, interstitial fibrosis (ci) was observed as the strongest association with serum UA levels (p = 0.022). Our observations broaden our current understanding of contributory metabolic factors that influence the initial disease course in ANCA-associated renal vasculitis.