The NEPHRO-IBD study is a multicenter prospective observational study designed to evaluate the prevalence of renal dysfunction and renal complications in adult patients with inflammatory bowel disease (IBD) compared with individuals from the general population. Although extraintestinal manifestations are common in IBD, renal involvement remains relatively underrecognized and insufficiently studied.

The study will recruit approximately 6,000 participants, including 3,000 patients with confirmed IBD (Crohn's disease or ulcerative colitis) and 3,000 individuals without IBD serving as a control group. Participants will undergo routine clinical assessment, including laboratory tests, urinalysis with measurement of the albumin-to-creatinine ratio (ACR), and imaging evaluation of the kidneys and urinary tract. Disease activity in patients with IBD will be assessed using validated clinical indices.

The study will also evaluate the relationship between renal dysfunction and disease activity, medications used in IBD treatment, and comorbidities. The results of this study are expected to improve the understanding of renal complications in patients with IBD and support earlier identification and management of kidney disease in this population.

Inflammatory bowel diseases (IBD), including Crohn's disease and ulcerative colitis, are chronic inflammatory disorders of the gastrointestinal tract that are frequently associated with extraintestinal manifestations. These manifestations may involve multiple organ systems, including the musculoskeletal, dermatologic, hepatobiliary, ocular, and renal systems. While several extraintestinal manifestations of IBD have been well described, renal complications remain relatively underrecognized and insufficiently investigated.

Renal manifestations associated with IBD may include nephrolithiasis, amyloidosis, tubulointerstitial nephritis, glomerulonephritis, urinary tract fistulas, and urothelial malignancies. In addition to disease-related mechanisms, potential contributing factors include immune dysregulation, genetic susceptibility, environmental factors, and nephrotoxic effects of medications used in the treatment of IBD, such as 5-aminosalicylates or thiopurines.

Previous studies suggest that patients with IBD may have an increased risk of chronic kidney disease (CKD) and acute kidney injury (AKI). However, the true prevalence and determinants of renal dysfunction in patients with IBD remain unclear due to limited prospective data.

The NEPHRO-IBD study is a multicenter prospective observational study designed to evaluate the prevalence of renal dysfunction and renal complications in adult patients with inflammatory bowel disease compared with individuals from the general population. Approximately 6,000 participants will be included, including 3,000 patients with confirmed IBD and 3,000 individuals without IBD serving as a control group.

Participants will undergo clinical assessment and routine laboratory testing at baseline and during follow-up visits performed at intervals of approximately three months. The evaluation will include blood tests, urinalysis with measurement of the urine albumin-to-creatinine ratio (ACR), and imaging assessment of the kidneys and urinary tract using abdominal ultrasound. In patients with IBD, disease activity will be evaluated using validated clinical indices, including the Total Mayo Score for ulcerative colitis and the Crohn's Disease Activity Index (CDAI). Fecal calprotectin levels will also be measured to assess intestinal inflammation.

The study will also investigate potential associations between renal abnormalities and inflammatory bowel disease activity, pharmacological treatment, and comorbid conditions. Early identification of renal dysfunction may facilitate timely nephrological evaluation and implementation of nephroprotective therapy in affected patients.

The results of the NEPHRO-IBD study are expected to improve understanding of renal involvement in inflammatory bowel disease and support the development of strategies for early detection and management of kidney disease in this population.

Inclusion Criteria:

• Age over 18 years
• Confirmed IBD based on the overall clinical picture and endoscopic examination, or no IBD (control group without IBD)
• Consent to participate in the study
• Cognitive abilities sufficient to complete the questionnaires

Exclusion Criteria:

• diabetes

• dysuric symptoms suggestive of urinary tract infections

• in women, menstruation (urinalysis can be performed 3 days before the onset and 3 days after the end of menstruation)

• refusal to participate in all procedures performed in the study

• age under 18 or over 80

• pregnancy

• other serious comorbidities whose presence or exacerbation may cause abnormalities in laboratory tests suggesting kidney disease

• previous surgery whose presence may cause abnormalities in laboratory tests suggesting kidney disease

• extreme physical exertion within 7 days before the test (marathons, half-marathons, triathlons) and intense physical exertion - strength training - within 1 day before the test. [moderate physical exertion such as walking, swimming, or cycling is not a contraindication]. • Excessive alcohol consumption 14 days before the study

• Inability to perform necessary tests: e.g., inability to perform an imaging test

• Unavailability of data: if the study is based on registry data, exclusion of individuals for whom there is incomplete data

• Dehydration

• Use of nephrotoxic medications* within a month before and during the study

• Use of angiotensin inhibitors, sartans, or flozins that were introduced into treatment within <3 months

  *Nephrotoxic drugs:

• Nonsteroidal anti-inflammatory drugs (NSAIDs) - occasional use is not contraindicated, but use for ≥ 10 days is an exclusion criterion

• Gold salts

• Penicillamine

• Interferon alpha

• Antituberculosis drugs (rifampicin, ethambutol, isoniazid)

• Pamidronate

• Biseptol

• Antiviral drugs (acyclovir)

• Anticonvulsants (carbamazepine, diazepam, phenobarbital)

• Cyclosporine A, tacrolimus

• Chinese herbs

• Oncology drugs (cisplatin)

The study population will consist of adult participants recruited at multiple gastroenterology centers in Poland. The study will include approximately 6,000 individuals, including 3,000 patients with confirmed Inflammatory Bowel Disease (Crohn's disease or ulcerative colitis) and 3,000 individuals without IBD serving as a control group from the general population.

Patients with IBD will be identified based on clinical evaluation and endoscopic confirmation of disease. Control participants will include adults without a diagnosis of inflammatory bowel disease who meet the study eligibility criteria.

All participants will undergo clinical assessment, laboratory testing including blood tests and urinalysis with measurement of the albumin-to-creatinine ratio (ACR), and abdominal ultrasound evaluation of the kidneys and urinary tract. In patients with IBD, disease activity will additionally be assessed using validated clinical indices.

De-identified individual participant data may be available upon reasonable request from the principal investigator.