What are the differential diagnoses for a 16-year-old with 7 months of abdominal pain and nausea, no NSAID use, normal imaging, normal complete blood count, and low serum creatinine?

Differential Diagnoses for a 16-Year-Old with Chronic Abdominal Pain and Nausea

The most likely diagnosis is functional dyspepsia (FD), potentially with overlapping irritable bowel syndrome (IBS), given the 7-month duration, normal imaging, and normal CBC in a 16-year-old without alarm features. 1, 2

Primary Differential Considerations

Functional Dyspepsia (Most Likely)

• FD is highly probable when epigastric pain or burning, early satiation, and/or postprandial fullness are present for ≥8 weeks with normal investigations 1
• The absence of alarm features (no weight loss, normal imaging, normal CBC) strongly supports this diagnosis in a 16-year-old 1
• Up to 50% of FD patients also meet criteria for IBS, so overlapping symptoms of altered bowel habits should be explored 1, 2
• Pain unrelated to defecation distinguishes FD from IBS, though both can coexist 1

Post-Infectious Functional Dyspepsia

• Accounts for approximately 10% of FD cases and should be screened for by asking about recent acute gastroenteritis 1, 2
• Associated pathogens include Norovirus, Giardia lamblia, Salmonella, E. coli O157, and Campylobacter 1

Gastroesophageal Reflux Disease (GERD)

• Coexists in approximately one-third of FD patients 1
• A burning sensation starting in the epigastrium but radiating to the chest helps differentiate GERD heartburn from dyspeptic epigastric pain 1

Eating Disorders or Disordered Eating Behavior

• Increasingly recognized in FD patients, particularly adolescents 1
• Should be specifically screened for in this age group 1

Helicobacter pylori-Associated Dyspepsia

• Must be excluded before confirming FD diagnosis 1, 2
• If H. pylori is positive, symptoms persisting after successful eradication then qualify as FD 1

Less Likely but Important Considerations

Celiac Disease

• Coeliac serology is indicated when dyspepsia overlaps with IBS-type symptoms 1, 2
• Should be tested given the chronic nature and nausea 1, 2

Biliary Colic

• Should be considered with episodic epigastric pain, especially if obesity is present 2
• Abdominal ultrasound is recommended for epigastric pain <1 year duration with biliary colic characteristics 1, 2

Psychological Factors

• Anxiety is associated with future development of FD in longitudinal studies 1
• Presence of other non-gastrointestinal chronic painful or functional disorders supports FD diagnosis 1

Clinical Context of Low Creatinine

The low creatinine finding is not diagnostically significant for the abdominal complaints in this clinical scenario. Low serum creatinine typically reflects:

• Low muscle mass (common in adolescents, particularly females) 3
• Nutritional status or eating patterns 3
• This does not suggest renal pathology causing the abdominal symptoms, as renal disease elevates creatinine 4, 5

Essential Next Steps in Evaluation

Mandatory Baseline Investigations

• Full blood count (already done—normal) 1, 2
• H. pylori testing via breath or stool test (essential before confirming FD) 1, 2
• Coeliac serology (indicated given chronic symptoms with nausea) 1, 2
• Abdominal ultrasound if biliary colic characteristics are present 1, 2

Endoscopy Considerations

• Non-urgent endoscopy should be considered for treatment-resistant dyspepsia in patients ≥25 years 1
• At age 16, endoscopy is NOT indicated in the absence of alarm features (weight loss, dysphagia, hematemesis, family history of gastroesophageal cancer) 1
• Urgent 2-week wait endoscopy is reserved for dyspepsia with weight loss if age ≥25 years 1

Critical History Elements to Clarify

• Relationship of pain to meals (induced by, relieved by, or occurring while fasting) 1, 2
• Relationship of pain to defecation (if related, consider IBS; if unrelated, supports FD) 1
• History of recent acute gastroenteritis (suggests post-infectious FD) 1, 2
• Presence of anxiety, stress, or psychological triggers 1
• Eating patterns and possible disordered eating 1
• Family history of gastroesophageal cancer, inflammatory bowel disease, or celiac disease 1

Common Pitfalls to Avoid

• Do not pursue extensive imaging or endoscopy in the absence of alarm features, as this delays diagnosis and increases patient anxiety 1
• Do not diagnose FD until H. pylori is excluded and treated if positive 1, 2
• Do not overlook overlapping IBS, which occurs in up to 50% of FD patients 1, 2
• Do not dismiss psychological factors—anxiety and stress are legitimate pathophysiologic contributors requiring specific management 1
• Do not attribute symptoms to low creatinine—this reflects muscle mass or nutrition, not a cause of abdominal pain 3