Crohn’s disease is a chronic inflammatory condition primarily affecting the digestive tract, causing inflammation anywhere from the mouth to the anus. Although symptoms center on the gut, the disease is systemic and can impact organs outside the digestive system. Kidney problems are related to Crohn’s, often indirectly. Complications arise from metabolic changes, chronic inflammation, and medication side effects.
Kidney Stone Formation
Patients with Crohn’s disease, especially those who have undergone small intestine surgery, face an increased risk of developing calcium oxalate kidney stones. This is caused by enteric hyperoxaluria, a metabolic complication altering how the body handles dietary oxalate. Normally, calcium in the gut binds to oxalate from food and is excreted in the stool.
Damage or surgical removal of the ileum can lead to fat malabsorption. Unabsorbed fatty acids travel to the colon, where they bind to free calcium, sequestering it. This leaves oxalate unbound, allowing it to be hyperabsorbed into the bloodstream.
Oxalate travels to the kidneys, combining with urinary calcium to form crystals and stones. Stones can cause flank pain and may obstruct urine flow, stressing the kidney. Chronic dehydration, common due to persistent diarrhea, further concentrates the urine and increases crystal formation.
Systemic Inflammation and Tissue Damage
The chronic inflammation defining Crohn’s disease affects the kidneys through mechanisms beyond stone formation. Persistent inflammation causes the release of circulating inflammatory proteins. In rare cases, this leads to secondary amyloidosis, where abnormal protein fragments deposit in the kidneys’ filtering units, impairing function.
Another inflammatory effect is immune-mediated tissue damage, such as glomerulonephritis or interstitial nephritis. Glomerulonephritis is inflammation of the glomeruli, reducing the kidney’s ability to clear waste. Interstitial nephritis affects the tubules and surrounding tissue, interfering with the kidney’s ability to concentrate urine and manage electrolytes.
Chronic diarrhea, a hallmark of active Crohn’s disease, leads to long-term renal stress. The persistent loss of fluid and electrolytes results in chronic dehydration, which stresses the kidneys and reduces blood flow. This chronic stress contributes to acute kidney injury and a decline in overall renal function.
Medication-Related Kidney Damage
A major cause of kidney problems is the potential nephrotoxicity of management drugs. Immunosuppressants (cyclosporine and tacrolimus) can damage small kidney blood vessels, potentially leading to chronic kidney injury. The 5-aminosalicylate class (mesalamine) can cause interstitial nephritis, an allergic reaction causing kidney tissue inflammation.
Certain antibiotics, such as metronidazole, used for abscesses or fistulas, carry a risk of temporary or permanent kidney damage. Patients must be cautious about using over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs), as they can cause acute kidney injury, especially if the patient is dehydrated. Patients must take prescribed medications only and ensure their physician is aware of all over-the-counter drug use.
Regular monitoring is necessary when taking potentially nephrotoxic drugs to detect damage early. Avoiding self-medication with NSAIDs is an important step to protect kidney function.
Recognizing and Monitoring Kidney Health
Proactive monitoring is necessary because kidney problems often develop slowly without obvious symptoms. Subtle changes may manifest as persistent fatigue, swelling (edema) in the legs or around the eyes, or high blood pressure. More specific signs include changes in urine output, flank pain suggestive of a stone, or blood in the urine.
Physicians monitor kidney health using standard diagnostic tools that assess filtering waste. These include a blood test to measure serum creatinine and calculate the estimated glomerular filtration rate (eGFR), which indicates filtering efficiency. A urinalysis is also standard, looking for protein or blood in the urine, which signals damage to the filtering units.
Management strategies focus on reducing the risk factors unique to Crohn’s disease. Maintaining adequate hydration is a highly effective measure to prevent urine concentration and stone formation. Dietary modifications, such as reducing high-oxalate foods, may be recommended for patients with enteric hyperoxaluria. Regular dialogue with a gastroenterologist and a kidney specialist ensures kidney health remains a priority.