Sixty-nine publications were included for this review, among which 38 were from mainland China (2015–2021) [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48], 15 from Japan (2003–2021) [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63], 10 from South Korea (2010–2020) [64,65,66,67,68,69,70,71,72,73], 3 from Taiwan (2014–2019) [74,75,76], and 3 from Australia (2001–2021) [77,78,79]; characteristics of the studies are shown in Supplementary Table S2. Approximately 83% the publications reported a retrospective study design (n = 57). For publications from mainland China, sample sizes ranged from 74 [37] to 4,367,829 [47], and male percentages ranged from 37.5% [17] to 97.3% [32]. For publications from Japan, sample sizes ranged from 52 [53] to 270,902 [63]; the male percentage ranged from 37.1% [58] to 56.96% [52]. For publications from South Korea, sample sizes ranged from 25 [64] to 5,114 [67]; the male percentage ranged from 36% [64] to 66.6% [73]. For publications from Taiwan, sample sizes ranged from 91 [75] to 7,073 [76]; the male percentage ranged from 45.9% [76] to 52.7% [75]. For publications from Australia, sample sizes ranged from 1,147 [78] to 2,457 [79]; the male percentage ranged from 60% [77] to 69.7% [79]. The Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline [1] and 2 country-specific guidelines [80, 81] were also included for evidence on treatment patterns.

Sixty-eight journal articles were assessed for study quality (all details of the quality assessment are shown in Supplementary Table S3); one white paper was not included in the study quality assessment. Approximately 75% (51/68 articles) were deemed to be of good quality (i.e., without inherent flaws). Few studies reported the incidence/prevalence of IgAN directly and percentage of IgAN were extracted from included studies. The appropriateness of the statistical analysis conducted was not clear or not specified in 5 studies, as they did not define P values and the level of significance for all observations. Across studies, outcome measures were generally considered reliable. However, 33 articles stated that the results could be generalized to routine practice. In one case-control study, the similarity of both groups at the outset of the study was not clear.

Six publications provided evidence on IgAN incidence [30, 61, 63, 74, 77, 78] in Australia (n = 2), Japan (n = 2), mainland China (n = 1), and Taiwan (n = 1). Most were cross-sectional observational studies (n = 4), and sample sizes ranged from 156 [74] to 270,902 [63].

In Australia, IgAN incidence was estimated to be 1.41–10.5 per 100,000 people per year [77, 78]. According to Briganti 2001 [78], IgAN incidence in Australia was lowest (0.0 per 100,000 per year) among male children and highest (10.7 per 100,000 per year) among male adults [78]. In Japan, only 2 studies reporting incidence data among children were identified. Utsunomiya 2003 [63] reported an incidence rate of 4.5 per 100,000 per year among 270,902 junior high and elementary school students; Kajiwara 2020 [61] reported a rate of 3.3 per 100,000 per year among 60,816 junior high and elementary school students. Both publications collected urine samples through a school urinary screening system in students 6 to 15 years old. In mainland China, the incidence rate of IgAN was estimated to be 6.3% among elderly patients who underwent renal biopsy and 24.7% among non-elderly patients who underwent renal biopsy [30]. In Taiwan, IgAN incidence was estimated to be 5.5 per million per year among the general population (around 23.5 million between 2014 and 2016), based on 1,445 renal biopsy records from a registry database [74]. In general, IgAN incidence was higher in males (5.7 per 100,000 per year) compared with females (2.9 per 100,000 per year) [78]. IgAN incidence was not reported in Korean populations.

IgAN prevalence among the general population was not reported in the included publications. But one cross-sectional study (n = 3,623) reported an IgAN prevalence rate of 0.03% among the general Chinese pediatric population [34]. Thirty-five publications were identified with diagnosis rates among 2 populations: patients who received renal biopsies and PGN patients [13, 14, 17,18,19, 21, 22, 24, 30, 31, 33,34,35,36, 39, 40, 43,44,45,46,47,48, 52, 59, 67,68,69