Dialysis is a life-sustaining medical treatment that removes excess fluid, waste products, and toxins from the blood when kidneys fail. Gastrointestinal (GI) symptoms are common among patients with Chronic Kidney Disease (CKD) and those receiving kidney replacement therapy. Determining if the dialysis procedure itself causes diarrhea is complex, as underlying kidney failure, medications, and the treatment process all contribute. This article explores the direct procedural effects of dialysis and the numerous non-procedural factors that frequently lead to diarrhea in the kidney patient population.
Direct Impact of Dialysis on Gastrointestinal Health
The procedure of hemodialysis (HD) involves the rapid removal of fluid, which triggers significant fluid shifts and electrolyte imbalances. This rapid change can irritate the gastrointestinal tract, potentially resulting in diarrhea. Furthermore, intense fluid removal during HD can sometimes lead to transient episodes of low blood pressure, which temporarily reduces blood flow to the intestines. This reduced circulation can make the bowel more susceptible to irritation or even damage, a condition known as ischemic colitis.
Chronic kidney failure creates a toxic environment, known as the uremic milieu, which fundamentally alters gut health. Uremic toxins damage the mucosal lining, increasing intestinal permeability and leading to a “leaky gut.” This impaired barrier function leads to dysmotility, or abnormal movement of the bowel. While dialysis removes these toxins, the rapid correction of this uremic state during the treatment may temporarily influence gut motility, further contributing to bowel irregularity.
Peritoneal dialysis (PD) introduces a highly concentrated sugar solution, the dialysate, directly into the abdominal cavity. This fluid is hyperosmolar, meaning it draws water and waste across the peritoneal membrane. The hyperosmolar nature of the dialysate affects the fluid dynamics of the intestines in close proximity. This osmotic effect may alter the water content within the bowel lumen, contributing to changes in stool consistency.
The physical presence of several liters of dialysate fluid in the abdomen also creates mechanical pressure on the stomach and intestines. This pressure can slow gastric emptying and displace the bowel, which may disrupt normal peristaltic movement and lead to various GI symptoms, including loose stools. The constant state of systemic inflammation associated with CKD and dialysis drives changes in the gut microbiome, known as dysbiosis. This imbalance of gut bacteria can impair motility and exacerbate inflammation in the intestinal lining, promoting digestive distress.
Non-Procedural Causes of Diarrhea in Kidney Disease Patients
Medications are one of the most frequent non-procedural causes of diarrhea in the CKD population. Phosphate binders, prescribed to control high phosphorus levels, are a major culprit. Their mechanism involves binding phosphate in the gut to prevent absorption. Certain non-calcium-based binders, such as sevelamer carbonate, have a documented rate of diarrhea as a side effect, affecting approximately 21% of users. Similarly, the iron-based binder ferric citrate also frequently lists diarrhea among its gastrointestinal side effects.
Antibiotics are often necessary for treating infections, but they can dramatically disrupt the balance of the gut microbiome. This microbial imbalance can lead to antibiotic-associated diarrhea, and in severe cases, can trigger an overgrowth of the bacterium Clostridioides difficile (C. difficile), which causes severe, infectious diarrhea. Many patients also take iron supplements to manage anemia, and high-dose oral iron can directly irritate the GI tract, leading to abdominal discomfort and loose stools.
Pre-existing conditions frequently seen in kidney patients also contribute significantly to diarrhea. Diabetes, the leading cause of kidney failure, can lead to a complication called diabetic enteropathy. This condition is caused by long-term nerve damage (autonomic neuropathy) affecting the nerves that control the digestive system. This results in abnormal gut motility and chronic diarrhea, often alternating with periods of constipation.
Dietary restrictions imposed by CKD management can unintentionally contribute to digestive issues. Limiting high-potassium and high-phosphorus foods can result in a diet that is low in fiber, which is important for healthy bowel function. Furthermore, some patients consume artificial sweeteners, such as sorbitol, found in sugar-free products, which are poorly absorbed and can trigger an osmotic laxative effect, resulting in diarrhea. Infectious causes, including common viral or bacterial gastroenteritis, are also more serious for kidney patients due to a generally weakened immune system.
Practical Management and When to Contact Your Care Team
When experiencing persistent changes in bowel habits, tracking the frequency, consistency, and timing of the stools is a helpful first step. Note whether the diarrhea occurs shortly after a dialysis session or following a specific meal or medication dose. This detailed information is important for the care team to pinpoint the likely cause. Simple dietary adjustments can often help manage mild diarrhea by temporarily focusing on bland, low-fiber, binding foods like white rice, bananas, and toast. Maintaining adequate fluid intake is important to prevent dehydration, but this must be done carefully within the strict fluid limits prescribed by the nephrology team.
Never stop taking prescribed medications, especially phosphate binders, without first consulting with the nephrology team or a dietitian. These medications are important for controlling phosphorus levels and protecting bone health, and abruptly discontinuing them can lead to serious health consequences. A healthcare provider may be able to adjust the dose, switch to a different binder, or suggest an alternative medication to manage the side effects.
Severe, persistent diarrhea requires immediate medical attention to prevent serious complications. It quickly leads to dangerous dehydration and electrolyte imbalances, which can cause acute kidney injury. Seek immediate care if the diarrhea is accompanied by:
- Fever
- Blood in the stool
- Severe abdominal pain
- Signs of severe dehydration such as excessive thirst, dizziness, or passing very little urine
Diarrhea that lasts longer than 48 hours should also be reported to the care team promptly.