What is the best course of action for a 20-year-old patient with chronic right-sided abdominal pain, constipation, altered bowel movements, and hot flashes after eating, who has a history of smoking legal weed and has had multiple ER visits and a normal upper abdominal ultrasound, as well as a negative H. pylori (Helicobacter pylori) test?

Diagnostic Workup for Young Adult with Chronic Right-Sided Abdominal Pain and Altered Bowel Habits

This 20-year-old patient requires immediate celiac disease testing (tissue transglutaminase IgA with total IgA level), complete blood count with ferritin, fecal calprotectin, and colonoscopy with biopsies to exclude organic disease before attributing symptoms to functional dyspepsia or irritable bowel syndrome. 1

Critical Initial Laboratory Testing

The combination of chronic abdominal pain, altered bowel movements (change in appearance, color, smell), and constipation in a young patient warrants specific testing to exclude serious organic pathology:

• Celiac disease screening is mandatory with tissue transglutaminase IgA antibodies plus total IgA level, as celiac disease commonly presents with chronic abdominal symptoms and altered bowel habits 1
• Complete blood count with ferritin must be obtained immediately, as microcytic anemia would constitute an alarm feature requiring urgent colonoscopy 1
• Fecal calprotectin testing is essential to exclude inflammatory bowel disease, particularly given the chronic nature and bowel habit changes 1
• Coeliac screening is specifically recommended in patients with IBS-type symptoms and overlapping features 2

Endoscopic Evaluation Required

Colonoscopy with biopsies is mandatory despite the patient's young age because the combination of chronic right-sided abdominal pain, altered bowel characteristics, and persistent symptoms after multiple ER visits constitutes alarm features that require exclusion of colorectal pathology 1:

• Right and left colon biopsies (not rectal) should be obtained to exclude microscopic colitis, which presents with chronic abdominal complaints and altered bowel habits 1
• The change in stool appearance, color, and smell represents a significant bowel habit change that persists beyond 2 weeks, warranting investigation 2, 3
• Microcytic anemia (if present) should never be attributed to dietary deficiency alone without excluding gastrointestinal pathology 1

Additional Diagnostic Considerations

• Thyroid function tests (TSH) should be performed to exclude hyperthyroidism as a cause of altered bowel habits and the reported "hot flashes" 1
• Stool occult blood testing (fecal immunochemical test) if not already completed 1
• Inflammatory markers (CRP or ESR) should be checked, as a normal CRP combined with negative calprotectin almost certainly rules out inflammatory bowel disease 4

Functional Disorder Evaluation After Negative Workup

If all organic causes are excluded, consider functional dyspepsia or irritable bowel syndrome:

• The right-sided location, postprandial symptoms ("feels funny after eating"), and constipation pattern suggest possible IBS with constipation predominance 2, 5
• The "hot flashes" when stomach hurts may represent visceral hypersensitivity or autonomic dysfunction seen in disorders of gut-brain interaction 2, 6
• Cannabis use history is relevant, as it can alter gut motility and potentially contribute to functional symptoms, though this temporal relationship (one year ago) makes direct causation less likely 2

Management Algorithm Based on Test Results

If celiac serology is positive:

• Upper endoscopy with small bowel biopsies is required for definitive diagnosis before starting gluten-free diet 1
• Do not start dietary modifications before biopsy confirmation 1

If inflammatory markers or calprotectin are elevated:

• Proceed urgently with colonoscopy and consider inflammatory bowel disease workup 1

If all testing is negative:

• Establish diagnosis of functional disorder (IBS or functional dyspepsia) based on Rome IV criteria 2, 5
• Begin therapeutic trial with fiber supplementation for constipation 2
• Consider antispasmodic medication for meal-related pain 2
• Provide education about gut-brain axis and reassurance that normal tests do not mean symptoms are not real 2

Critical Pitfalls to Avoid

• Never delay colonoscopy based on age alone when alarm features are present (persistent symptoms, bowel habit changes, right-sided pain) 1
• Do not perform celiac testing after starting gluten-free diet, as this causes false-negative results 1
• Avoid attributing symptoms to cannabis use from one year ago without excluding current organic pathology 2
• Do not diagnose IBS without first excluding celiac disease and inflammatory bowel disease in patients with overlapping symptoms 2, 1
• Rectal bleeding or persistent constipation beyond 7 days requires medical evaluation and should not be managed with over-the-counter fiber alone 7, 3

Immediate Next Steps

1. Order celiac panel (tTG-IgA + total IgA), CBC with ferritin, CRP/ESR, fecal calprotectin, TSH, and fecal immunochemical test 2, 1
2. Refer for colonoscopy with biopsies regardless of laboratory results given chronic symptoms and alarm features 1
3. If celiac serology positive, arrange upper endoscopy before any dietary changes 1
4. Establish therapeutic relationship and explain that thorough evaluation is necessary before attributing symptoms to functional disorder 2