What is the appropriate evaluation and treatment for an adult patient with yellow stool and bubbles, considering their past medical history and potential gastrointestinal conditions?

Yellow Stool with Bubbles: Evaluation and Management

Yellow, frothy (bubbly) stool suggests fat malabsorption or rapid intestinal transit, and you should evaluate for steatorrhea, bile acid malabsorption, pancreatic insufficiency, small bowel disease, or infectious causes with targeted testing based on symptom duration and severity.

Initial Clinical Assessment

The appearance of yellow, bubbly stool indicates either:

• Fat malabsorption (steatorrhea) - causing pale, greasy, floating stools with bubbles
• Bile acid malabsorption - causing yellow-green, watery diarrhea
• Rapid transit through the intestines - preventing normal bile processing

Key Historical Features to Elicit

• Duration: Acute (<4 weeks) vs chronic (>4 weeks) determines the diagnostic pathway 1
• Associated symptoms: Weight loss, abdominal pain, fever, or blood suggest organic disease requiring urgent evaluation 1
• Medication history: Recent antibiotics raise concern for C. difficile infection or antibiotic-associated diarrhea 2
• Dietary patterns: High fat intake, lactose consumption, or recent dietary changes 1
• Risk factors: Age >50, family history of inflammatory bowel disease or celiac disease, immunosuppression 1

Diagnostic Approach Based on Duration

For Symptoms <4 Weeks (Acute)

First-line testing:

• Stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter) 1, 2
• C. difficile toxin testing if recent antibiotic use, fever, abdominal pain, or leukocytosis 2
• Complete blood count, inflammatory markers (CRP) 1

Do not perform extensive malabsorption workup for acute symptoms unless severe or persistent 1

For Symptoms >4 Weeks (Chronic)

This requires systematic evaluation for malabsorption:

Mandatory initial blood tests 1:

• Complete blood count (anemia suggests malabsorption)
• Celiac serology (tissue transglutaminase IgA with total IgA)
• Inflammatory markers (CRP, ESR)
• Thyroid-stimulating hormone (hyperthyroidism causes rapid transit)

Stool studies 1:

• Fecal elastase to assess pancreatic function - this is the preferred test for pancreatic insufficiency 1
• Fecal calprotectin if age 16-40 to exclude inflammatory bowel disease (>250 μg/g warrants urgent gastroenterology referral) 1
• Stool culture if not already done

Second-line testing for persistent symptoms 1:

• SeHCAT scan or serum 7α-hydroxy-4-cholesten-3-one for bile acid malabsorption - this should be done in all patients with functional diarrhea or IBS-diarrhea pattern 1
• Hydrogen breath testing for lactose maldigestion if suspected 1
• Colonoscopy with biopsies from right and left colon (not rectum) to exclude microscopic colitis 1

Advanced imaging if above tests negative 1:

• MR enterography (preferred over CT) to evaluate small bowel for Crohn's disease, lymphoma, or structural abnormalities 1
• Video capsule endoscopy if MR enterography inconclusive 1

Common Pitfalls to Avoid

• Do not perform barium studies - they have poor sensitivity and specificity for small bowel disease 1
• Do not routinely test for small intestinal bacterial overgrowth with breath testing - instead, use an empirical trial of antibiotics if suspected 1
• Do not order metabolic panels (calcium, glucose) routinely unless other clinical features suggest endocrine disease 1
• Do not delay colonoscopy in patients >50 years with new-onset symptoms or any patient with alarm features (weight loss, blood, anemia) 1

Immediate Management While Awaiting Results

Dietary modifications:

• Trial of lactose-free diet for 2 weeks 1, 3
• Reduce dietary fat intake 3
• Avoid caffeine and alcohol 3
• Maintain adequate hydration with 8-10 glasses of clear liquids daily 2

Symptomatic treatment (only after excluding infection):

• Loperamide 4 mg initially, then 2 mg every 2-4 hours (maximum 16 mg/day) for non-bloody diarrhea 1, 2
• Do not use antimotility agents if fever, bloody stool, or suspected C. difficile infection 1

When to Refer Urgently

Immediate gastroenterology referral or colonoscopy 1:

• Age >50 with new-onset symptoms and no recent colorectal cancer screening
• Rectal bleeding with altered bowel habit
• Unintentional weight loss
• Iron deficiency anemia
• Fecal calprotectin >250 μg/g
• Persistent symptoms despite initial treatment

Hospital admission if 1:

• Severe dehydration with orthostatic symptoms
• Fever with severe abdominal pain
• Signs of acute severe colitis (>6 bloody stools/day with systemic toxicity)

The yellow, bubbly appearance specifically suggests you should prioritize testing for fat malabsorption (fecal elastase) and bile acid malabsorption (SeHCAT or serum 7α-hydroxy-4-cholesten-3-one) once infectious causes are excluded 1.