Background and Aims ANCA-associated vasculitis is a group of autoimmune vasculitides of unknown aetiology that predominantly affect small blood vessels among different organ systems, with different phenotypic manifestations. Although vasculitides were reported to account for 12 percent of all renal biopsies in the state of Victoria [1] and crescentic glomerulonephritis was reported to account for 6 percent of all renal biopsies in the state of Queensland [2], the epidemiology data on renal predominant ANCA vasculitis, particularly renal biopsy confirmed ANCA associated glomerulonephritis (AAGN) is limited.

Method This retrospective study was performed at the Royal Brisbane and Women's Hospital, a major tertiary hospital that service a population of 1,030,006 in North Brisbane, Australia. The 2012 Chapel Hill Consensus Conference definitions were used to identify renal predominant ANCA vasculitis. Patients with pauci-immune glomerulonephritis confirmed on kidney biopsy between 1st January 2005 to 1st October 2021 were selected. Clinical data was collected via electronic and paper medical records. Modified Monash Model classification was used to determine rurality of cases.

Results 1433 kidney biopsy results were reviewed. 80 cases of biopsy-confirmed pauci-immune AAGNs were identified. There was no significant difference in gender (Male; 42/80 (53%), p = 0.87). There was a preponderance towards MPO-positive AAGN (53/80), as opposed to PR3-positive disease (21/80), 5/80 were ANCA negative and 1/80 did not have ANCA serology available. The mean age of diagnosis was similar between MPO and PR3 (63.7 vs 59.5 years, p = 0.34) and between males and females (63.3 vs 59.3, p = 0.42). There was no seasonal variation in AAGN diagnoses – 23/80 in spring, 20/80 in summer, 14/80 in autumn, 23/80 in winter ( χ2 = 1.48, p = 0.69). Fourteen (18%) patients died during the study period, 3 of which died prematurely before age 65. Within our cohort, 16% (13/80) of cases lived in regional/rural areas. Interestingly, all 3 premature deaths were from these areas. This may reflect poorer access to health care in regional/rural settings.

Conclusion Pauci-immune ANCA-associated glomerulonephritis remains rare in North Brisbane, with estimated annual incidence of 4.6/million population, representing 5.6% of all kidney biopsies. The incidence is significantly lower than an American-based study that reported an incidence of 20 cases/million population [3] whilst a Swedish study reported an incidence of 13.2 cases/million population [4]. The reason behind the geoepidemiology variation is unclear, though there are evidence suggesting complex interaction of polygenic genetic susceptibility, epigenetic influences, and environmental associations such as rurality of living. Within our cohort, the incidence of MPO AAGN was 2.5 fold higher than PR3 AAGN, this is similar to other observed European and American data [5]. Our findings add to the current literature, particularly where epidemiological data on AAGN from the southern hemisphere is limited.