Supplementary Material for: Kidney Biopsy Findings and Clinical Outcomes of US Veterans with Inflammatory Bowel Disease

Introduction: Patients with inflammatory bowel disease (IBD; ulcerative colitis [UC], and Crohn’s disease [CD]) may have unique patterns of kidney injury related to their underlying or co-existing disease, or to medications. We present the kidney biopsy findings and clinical outcomes of veterans with UC or CD from the US department of Veteran’s Affairs (VA) health system. Methods: Histopathologic and clinical data were extracted by retrospective review of the VA electronic health record of patients with IBD and a kidney biopsy between 2000 and 2018. Incident end-stage kidney disease (ESKD) was defined as requirement of kidney replacement therapy. Statistical analyses were performed using SAS. Results: A total of 140 patients (UC:91 and CD:49) underwent kidney biopsy. The three most common diagnoses were IgA nephropathy (17.1%), diabetic nephropathy (14.3%), and acute interstitial nephritis (9.3%). Significant interstitial fibrosis, tubular atrophy and arteriosclerosis were present in 45% of biopsies. 26% of patients with UC and 20% of those with CD progressed to ESKD, with a mean time from kidney biopsy of 3.1 and 1.9 years, respectively. 45% of patients with UC and 34% of those with CD died, with a mean time from kidney biopsy of 4.3 and 4.6 years, respectively. Conclusion: Among US Veterans with IBD who underwent a kidney biopsy, IgA nephropathy, diabetic nephropathy, and interstitial nephritis were among the most common findings. Additionally, features of advanced kidney disease with rapid clinical progression to ESKD or death was observed. These findings suggest a delay and possibly a low rate of diagnosis.