What is the cause of an elevated stool pH of 7.8?

Causes of Stool pH 7.8

An elevated stool pH of 7.8 is most commonly caused by carbohydrate malabsorption, particularly from fermentable carbohydrates that reach the colon and undergo bacterial fermentation. This alkaline pH is significantly higher than the normal colonic pH range and indicates potential digestive or absorptive abnormalities.

Normal Stool pH Values and Physiological Context

• Normal stool pH typically ranges from 5.7 in the cecum to about 6.7 in the rectum 1
• The pH gradually increases along the gastrointestinal tract:
  • Stomach: Highly acidic
  • Duodenum: ~pH 6
  • Terminal ileum: ~pH 7.4
  • Cecum: pH drops to 5.7
  • Rectum: pH rises to 6.7

Primary Causes of Alkaline Stool (pH 7.8)

1. Carbohydrate Malabsorption

• Fermentable carbohydrates are the primary cause of altered stool pH 2
• Common culprits include:
  • Lactose intolerance (affects approximately 68% of the world's population)
  • Fructans in wheat products
  • Artificial sweeteners (sorbitol)
  • FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols)

2. Enzyme Deficiencies

• Lactase deficiency (lactose intolerance)
• Sucrase deficiency affecting sucrose-containing foods 2
• Pancreatic enzyme insufficiency (chronic pancreatitis, cystic fibrosis)

3. Small Bowel Bacterial Overgrowth (SIBO)

• Altered gut microbiota can change the fermentation patterns and pH
• Bacterial overgrowth can lead to alkaline stool due to ammonia production

4. Short Bowel Syndrome

• Altered transit time and absorption capacity
• Changes in bacterial flora that affect pH regulation 3
• Research shows pH plays an important role in ecological changes in colonic bacteria 3

5. Medication Effects

• Proton pump inhibitors
• Antibiotics that alter gut flora
• Antacids (especially those containing magnesium hydroxide)

6. Inflammatory Bowel Conditions

• Crohn's disease and ulcerative colitis can alter stool pH
• However, severe active cases typically show very low colonic pH values 1

Clinical Significance of Alkaline Stool pH

• Alkaline stool pH (>7.0) has been associated with increased risk of Clostridium difficile infection 4

  • In one study, 86.7% of C. difficile positive patients had stool pH >7.0
  • Only 4% of patients with stool pH ≤7.0 tested positive for C. difficile infection

• In critically ill patients, fecal pH outside the normal range (either too acidic or too alkaline) is associated with:

  • Increased mortality
  • Higher incidence of bacteremia 5
  • Altered organic acid profiles in stool

Diagnostic Approach

1. Food diary to identify potential trigger foods 2
2. Evaluate for enzyme deficiencies, particularly lactase
3. Consider testing for:
   • Small intestinal bacterial overgrowth
   • Malabsorption syndromes
   • Inflammatory bowel disease
   • C. difficile infection (particularly with alkaline stool)
4. Measure fecal organic acids:
   • Alkaline feces typically show decreased acetic acid
   • Propionic acid is markedly decreased in alkaline feces 5

Management Considerations

• Low-FODMAP diet to identify specific triggers 2
• Enzyme supplementation if deficiency is identified
• Treatment of underlying conditions (SIBO, IBD, etc.)
• Avoid combinations of foods known to cause digestive symptoms 2

Remember that while an alkaline stool pH of 7.8 is abnormal and warrants investigation, the specific cause needs to be determined through appropriate clinical evaluation and testing.