Extraintestinal Manifestations of Inflammatory Bowel Disease: A Focus on Kidney Complications

Inflammatory bowel disease (IBD), comprising Crohn’s disease (CD) and ulcerative colitis (UC), is a chronic relapsing–remitting condition characterized by systemic and intestinal inflammation and immune dysregulation. Up to 47% of IBD patients develop extraintestinal manifestations, yet kidney and urological involvement remain underrecognized. Accumulating evidence has linked IBD to nephrolithiasis, glomerular diseases, tubulointerstitial nephritis, acute kidney injury, chronic kidney disease, and, rarely, amyloid A amyloidosis. Population studies have consistently shown elevated risks for various important kidney disorders in IBD, with CD generally posing a greater risk than UC. The pathogenesis of kidney complications in IBD reflects complex gut–kidney interactions, including metabolic and absorptive abnormalities, shared genetic and immune pathways, intestinal dysbiosis with nephrotoxic microbial metabolites, systemic inflammation, and drug-related nephrotoxicity. Strategies for kidney protection in IBD include increased awareness, close monitoring of kidney function, urinary metabolic profiling in high-risk patients, and prompt nephrology referral for early detection and treatment. Management should include an effective and sustained control of intestinal inflammation, discontinuation of potential nephrotoxic drugs when indicated, and timely diagnosis and treatment of kidney manifestations, as well as integrating kidney complications into IBD guidelines to enhance awareness, ultimately optimizing both the kidney and overall outcomes for IBD patients. Future studies are needed to validate the potential predictive biomarkers for kidney complications and to develop targeted interventions to address shared gut–kidney pathogenic mechanisms in IBD.