Supplementary Material for: The burden of chronic kidney disease of undetermined etiology (CKDu) in a tertiary care public hospital in north India

Introduction: Chronic kidney disease of undetermined aetiology (CKDu) is an important public health problem. Indian data is mostly based on studies from rural regions in south and eastern India. We examined the burden and profile of CKDu in patients attending a tertiary care hospital in north India. Methods: We assessed records of consecutive new CKD patients registered in nephrology clinic from January 2015 till June 2022. Patients were classified as CKDu based on predefined inclusion and exclusion criteria. Clinical and laboratory parameters at presentation and kidney biopsy when done were noted. Results: Records of 32369 patients with CKD were screened, 29663 were included (2706 excluded due to inadequate data). 370 (1.2%) patients were categorized as CKDu. Mean age was 41±14.7 years, 58.1% being males. 158 (42.7%) patients were in CKD stage 3, 89 (24.1%) in stage 4, 84(22.7%) in stage 5 and 39(10.5%) were dialysis dependent at presentation. 232(62.7%) patients had proteinuria <0.5gm/day and 138(37.3%) between 0.5-1 gm/day. Renal histology was available for 65 CKDu patients :62 had chronic tubulointerstitial nephritis (CTIN) and 3 had non-specific changes. Conclusion: When defined using strict criteria with intensive diagnostic work-up, burden of CKDu is low in our hospital-based cohort of CKD patients. CTIN is the predominant histopathological finding in kidney biopsy.