What could be causing my stomach pain, nausea, bloating, and diarrhea?

Differential Diagnosis and Evaluation Approach

In a 29-year-old with stomach pain, nausea, bloating, and diarrhea, the most critical first step is to determine whether this represents acute infectious diarrhea (self-limiting) versus chronic symptoms requiring systematic investigation for organic disease including celiac disease, inflammatory bowel disease, or functional gastrointestinal disorders. 1

Immediate Assessment: Acute vs. Chronic Presentation

If symptoms are acute (< 4 weeks):

• Most cases are self-limiting viral gastroenteritis requiring no diagnostic workup 2
• Urgent evaluation is needed ONLY if you observe: 2
  • Signs of severe dehydration
  • Bloody stools
  • Persistent fever
  • Recent antibiotic use (consider Clostridium difficile) 1
  • Recent overseas travel 1
• For uncomplicated acute diarrhea, initiate early oral refeeding and consider antidiarrheal medications 2

If symptoms are chronic (≥ 4 weeks):

This requires systematic investigation as outlined below.

Red Flag Symptoms Requiring Urgent Gastroenterology Referral

Screen immediately for alarm features that indicate organic disease: 3, 4, 2

• Unintentional weight loss
• Gastrointestinal bleeding (visible blood or black tarry stools)
• Persistent vomiting
• Anemia on laboratory testing
• Palpable abdominal mass
• Family history of inflammatory bowel disease or colorectal cancer

If ANY red flags are present, refer urgently to gastroenterology before proceeding with outpatient workup. 3, 4, 2

Initial Laboratory Evaluation for Chronic Symptoms

Order these screening tests first, as abnormal results have high specificity for organic disease: 1, 5

Mandatory first-line tests:

• Complete blood count (to assess for anemia, which suggests malabsorption or inflammatory disease) 1, 5
• Comprehensive metabolic panel (low albumin or elevated inflammatory markers suggest organic disease) 1, 5
• Erythrocyte sedimentation rate (elevated ESR has high specificity for organic disease) 1
• Celiac disease serologic screening with tissue transglutaminase IgA antibody AND total IgA level (celiac disease is the most common small bowel enteropathy in the Western world and frequently presents with diarrhea, bloating, and nausea) 1, 4, 5
• Thyroid function tests (TSH, Free T4) (hyperthyroidism commonly causes diarrhea through endocrine effects and rapid gut transit) 1, 5
• Fecal calprotectin (to screen for inflammatory bowel disease, especially with abdominal pain and bloating) 5

Critical testing note:

The combination of GI symptoms with anemia represents alarm symptoms warranting urgent investigation, particularly for celiac disease which is present in 2-6% of patients with iron deficiency anemia. 4

Detailed History to Guide Further Workup

Medication and substance review:

• Up to 4% of chronic diarrhea cases are medication-induced 1
• Specifically ask about: magnesium-containing products, antihypertensives, NSAIDs, theophyllines, antibiotics, antiarrhythmics 1
• Alcohol abuse causes diarrhea through rapid gut transit, decreased disaccharidase activity, and pancreatic dysfunction 1
• Food additives: sorbitol and fructose 1

Dietary triggers:

• Ask specifically about lactose, fructose, and gluten consumption and correlation with symptoms 1, 3
• Artificial sweeteners (sugar alcohols, sorbitol) commonly cause bloating 1
• Carbohydrate malabsorption from lactase or sucrase deficiency causes osmotic diarrhea that typically worsens after meals 1

Bowel pattern characterization:

• Use Bristol Stool Scale to assess consistency 3
• Diarrhea alternating with constipation suggests irritable bowel syndrome 3
• Relationship between symptoms and meals (postprandial worsening suggests gastroparesis or bile acid malabsorption) 1, 3

Comorbid conditions:

• Diabetes mellitus (predisposes to diarrhea through autonomic dysfunction and bacterial overgrowth) 1
• Previous abdominal surgery (short bowel syndrome, bile acid malabsorption, bacterial overgrowth) 1
• Autoimmune diseases (increase celiac disease prevalence) 1

Differential Diagnosis by Symptom Pattern

If bloating and nausea predominate with diarrhea:

Consider gastroparesis, which presents with nausea, vomiting, bloating, postprandial fullness, early satiety, and abdominal pain 6, 7

• More common in diabetics but can be idiopathic 6
• Gastric emptying scintigraphy is the most validated assessment 6

If bloating is the primary complaint:

Functional bloating affects 3.5% of the general population (higher in women at 4.6%) 1

• However, bloating occurs in >50% of patients with IBS, constipation, and functional dyspepsia 1
• The positive predictive value of bloating for functional bowel disorder is 66% 8

If diarrhea is predominant:

Most common causes in young adults include: 1

• Celiac disease (most common small bowel enteropathy)
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• Microscopic colitis
• Bile acid malabsorption
• Small bowel bacterial overgrowth
• Lactase deficiency
• Giardiasis or other chronic infection

Management Algorithm Based on Initial Testing

If celiac serology is positive:

Proceed directly to upper endoscopy with duodenal biopsies for confirmation before starting gluten-free diet 4

If initial labs are normal and no red flags:

• Consider empiric trial of lactose-free diet for 2 weeks 1
• If symptoms persist, consider referral for colonoscopy with biopsies (to evaluate for microscopic colitis and inflammatory bowel disease) 1
• Consider breath testing for small intestinal bacterial overgrowth 1

If functional disorder is suspected after negative workup:

Brain-gut behavior therapy can improve symptom burden and quality of life in patients with functional GI symptoms 1

Common Pitfalls to Avoid

• Do not assume symptoms are functional without first screening for celiac disease—it is easily missed and highly treatable 1, 4
• Do not overlook medication review—this accounts for 4% of chronic diarrhea cases 1
• Do not dismiss bloating as benign—it has 66% positive predictive value for functional bowel disorders and significantly impairs quality of life 8
• Do not order extensive testing in acute diarrhea without red flags—most cases are self-limiting 2