What are the causes and treatments of green stool?

Green Stool: Causes and Clinical Significance

Green stool is a normal variation in healthy individuals, particularly in infants, and does not require treatment in the absence of other concerning symptoms. 1, 2

Normal Physiologic Causes

Infants and Children

• Nearly half (47.4%) of healthy term infants experience green stool as the dominant color for at least one week during the first 17 weeks of life, with comparable frequency between breastfed (47.7%) and formula-fed (45.2%) infants 1
• Green stools in infants are associated with higher defecation frequency and should be considered normal without signs of disease 1, 2
• Iron-fortified formulas (12 mg/L), particularly whey-predominant formulas, commonly produce green stools 2
• Higher bile acid concentrations (7.7 ± 1.52 mg/g dry weight) are found in green stools compared to brown stools (3.76 ± 0.7 mg/g dry weight), explaining the color variation 3

Adults

• Rapid intestinal transit allows bile pigments (biliverdin) to pass through before bacterial conversion to brown stercobilin 1
• Dietary factors including green vegetables (chlorophyll), food dyes, and iron supplements commonly cause green discoloration 2

When Green Stool Requires Evaluation

Red Flag Symptoms Requiring Investigation

Evaluate further only when green stool occurs with:

• Blood or mucus in stool 4
• Abdominal pain, cramping, or distention 4
• Fever 4
• Increased stool frequency (>4 stools/day over baseline) 4
• Weight loss or failure to thrive 4
• Anemia 4

Pathologic Conditions to Consider

In patients with diarrhea and green stools:

• Rule out infectious causes through stool culture and testing for inflammatory markers 4
• Consider bile acid malabsorption, particularly in patients with chronic diarrhea 3
• Evaluate for small intestinal bacterial overgrowth (SIBO) in appropriate clinical contexts 4

In cancer patients on immunotherapy:

• Green stool with increased frequency may indicate immune checkpoint inhibitor-induced colitis requiring endoscopic evaluation 4

Management Approach

Reassurance for Benign Cases

• No treatment is needed for isolated green stool without other symptoms 1, 2
• Educate patients and families that green stool represents normal variation in bowel function 1

Treatment When Pathology Identified

For chronic diarrhea with green stools and elevated bile acids:

• Cholestyramine or bismuth subsalicylate effectively decrease stool frequency and water content 3
• Bismuth subsalicylate is more effective at reducing water content than cholestyramine 3

For infectious diarrhea:

• Supportive care with loperamide is safe before microbiology results are available (unless neutropenic or suspected C. difficile) 4
• Treat identified pathogens appropriately per culture results 4

For SIBO contributing to symptoms:

• Sequential antibiotic therapy with poorly absorbable antibiotics (rifaximin preferred) or alternating cycles of metronidazole and tetracycline 4

Common Pitfalls to Avoid

• Do not assume green stool indicates infection or disease without accompanying symptoms 1, 2
• Avoid unnecessary testing (colonoscopy, extensive workup) in patients without alarm features 4
• Do not discontinue iron-fortified formula in infants solely due to green stool color 2
• In infants with occasional blood in stool (reported in 9.3% of healthy infants), do not immediately assume pathology without other concerning features 1