For a patient presenting with abdominal bloating and diarrhea, which laboratory tests should be ordered and what treatment is recommended?

Laboratory Testing and Treatment for Abdominal Bloating and Diarrhea

For a patient with abdominal bloating and diarrhea, you should order: (1) IgA tissue transglutaminase with total IgA level for celiac disease, (2) Giardia antigen test or PCR, and (3) fecal calprotectin to screen for inflammatory bowel disease. 1

Initial Laboratory Workup

The 2019 AGA guidelines provide clear, evidence-based testing recommendations for chronic diarrhea that directly apply to your patient:

Strong Recommendations (Must Order):

• Celiac disease testing: IgA tissue transglutaminase (IgA-tTG) with total IgA level

  • Sensitivity and specificity both >90% 1
  • If IgA deficient, add IgG tissue transglutaminase or IgG deaminated gliadin peptides 1
  • Positive results require duodenal biopsy confirmation 1

• Giardia testing: Antigen test or PCR (NOT ova and parasites)

  • Sensitivity and specificity >95% 1
  • This is a strong recommendation with high-quality evidence 1
  • Giardia is a common, readily treatable cause of watery diarrhea throughout the US 1

Conditional Recommendations (Should Consider):

• Fecal calprotectin or fecal lactoferrin to screen for inflammatory bowel disease
  • Use instead of ESR or CRP, which have poor diagnostic accuracy 1
  • If these tests are unavailable or not covered by insurance, CRP may be considered as a fallback option 1

Tests to AVOID:

• Do NOT order routine ova and parasites testing unless the patient has travel history to or recent immigration from high-risk areas 1
• Do NOT order ESR or CRP as primary IBD screening (conditional recommendation against) 1
• Do NOT order serologic tests for IBS diagnosis—they lack diagnostic accuracy 1

Additional Testing Based on Clinical Context

If Bloating is Prominent:

Per the 2023 AGA Clinical Practice Update on bloating 2:

• Carbohydrate enzyme deficiencies: Rule out with dietary restriction and/or breath testing 2
• Small intestinal bacterial overgrowth (SIBO): Only in at-risk patients, use small bowel aspiration or glucose/lactulose hydrogen breath testing 2
• Imaging and endoscopy: Order ONLY if alarm features present (bleeding, unexplained weight loss, age ≥45, nocturnal diarrhea, iron deficiency anemia) 2, 3

Consider Bile Acid Diarrhea Testing:

• Conditional recommendation to test for bile acid diarrhea 1
• Practical approach: Since specialized tests (48-hour stool bile acids, serum FGF-19) are not widely available, consider an empiric trial of bile acid binders (cholestyramine, colesevelam) 1
• Clinical response suggests bile acid diarrhea as the cause 1

Treatment Approach

First-Line Lifestyle Modifications:

Based on recent evidence 3:

• Regularly scheduled meals
• Exercise
• At least 8 cups of noncaffeinated fluids daily
• Limit caffeine to ≤3 cups daily
• Avoid alcohol and carbonated beverages

Dietary Interventions:

• Low FODMAP diet (fermentable oligosaccharides, disaccharides, monosaccharides, polyols) 3

  • Limit: legumes, wheat, onions, garlic, lactose, fructose, sorbitol, mannitol
  • Should be monitored by a gastroenterology dietitian 2
  • Improves symptoms in 50-80% of patients 3

• Do NOT use probiotics for bloating and distention 2

Pharmacologic Treatment:

For general chronic diarrhea management 3:

1. Opiate agonists: Loperamide (first-line antidiarrheal)
2. Anticholinergics: Hyoscyamine, dicyclomine
3. 5-HT3 antagonists: Ondansetron

These therapies improve diarrhea in 50-80% of patients 3

For Refractory Cases:

• Central neuromodulators (tricyclic antidepressants preferred over SSRIs) to reduce visceral hypersensitivity 2, 4
• Brain-gut behavioral therapies: Cognitive behavioral therapy, hypnotherapy, diaphragmatic breathing 2
• Biofeedback therapy if pelvic floor disorder identified 2

Common Pitfalls to Avoid:

1. Over-testing: Don't order comprehensive stool panels, gastric emptying studies, or whole gut motility studies unless specific indications exist 2
2. Missing celiac disease: Always include IgA-tTG testing—celiac disease is an important treatable cause 1
3. Ordering ova and parasites: This is low-yield without travel history; order Giardia-specific testing instead 1
4. Delaying empiric treatment: If initial workup is negative, the most likely diagnosis is IBS-D or functional diarrhea—treat empirically rather than pursuing endless testing 3

When to Escalate Testing:

Order colonoscopy with random biopsies if 3:

• Age ≥45 years
• Gastrointestinal bleeding
• Unexplained weight loss
• Nocturnal diarrhea
• Steatorrhea
• Iron deficiency anemia

Random biopsies during colonoscopy are essential to evaluate for microscopic colitis, which affects 13% of patients with chronic diarrhea despite normal endoscopic appearance 3.