Overview.
Chronic bloating is one of the most common and distressing gastrointestinal symptoms, affecting 16-30% of adults. While most cases are functional (IBS, dietary intolerance), bloating can be the presenting symptom of important underlying conditions including celiac disease, H. pylori infection, inflammatory bowel disease, hypothyroidism, and small intestinal bacterial overgrowth (SIBO). A strategic, symptom-guided laboratory workup can either identify a treatable cause or provide reassurance that symptoms are functional.
Bloating is the subjective sensation of increased abdominal pressure or tightness. Abdominal distension is the objective increase in girth. The two often coexist but can occur independently. Chronic bloating is defined as symptoms present for at least 3 months. Understanding the pathophysiology — whether driven by excess gas production, visceral hypersensitivity, impaired motility, or a structural cause — guides the diagnostic approach.
Prevalence: Chronic bloating affects 16-30% of the general population, with higher prevalence in women (~57% of sufferers). It is one of the top 5 reasons for gastroenterology referral and one of the most impactful GI symptoms for quality of life.
What to test.
First-line tests
- tTG-IgA + Total IgA — Celiac disease commonly presents as bloating, especially in adults without classic diarrhea. The ACG 2023 guideline recommends tTG-IgA testing in patients with IBS-like symptoms, especially with diarrhea component. Must check total IgA simultaneously.
- Complete Blood Count (CBC) — Screens for anemia (which can occur alongside celiac disease or IBD), infection, and reactive thrombocytosis (marker of active IBD).
- TSH (Thyroid-Stimulating Hormone) — Hypothyroidism slows gastrointestinal motility, causing bloating, constipation, and distension. A common, easily treatable cause of chronic GI symptoms.
- Comprehensive Metabolic Panel (CMP) — Screens for diabetes (gastroparesis risk), electrolyte imbalances, liver disease (ascites as cause of distension), and kidney function.
Second-line tests
- Fecal Calprotectin — The key test to differentiate IBD (Crohn's, UC) from IBS in patients with chronic GI symptoms. FC >150 μg/g indicates gut inflammation; FC <50 μg/g makes IBD unlikely. NOTE: this is a stool test, not a blood test.
- H. pylori Stool Antigen Test (or Urea Breath Test) — H. pylori is a common cause of upper GI bloating, early satiety, and functional dyspepsia. Testing indicated if upper abdominal bloating or epigastric discomfort is a prominent feature.
- HbA1c / Fasting Glucose — Diabetes-related gastroparesis causes severe post-meal bloating with nausea. Even pre-diabetes can impair gastric emptying.
- CRP / hs-CRP — Elevated CRP alongside bloating and diarrhea supports an inflammatory cause (IBD) rather than functional bowel disorder.
Specialized tests
- SIBO Breath Test (Hydrogen-Methane) — Small intestinal bacterial overgrowth (SIBO) is a common but underdiagnosed cause of severe post-meal bloating, particularly worsened by fermentable carbohydrates. A breath test measures exhaled hydrogen and methane after a carbohydrate challenge.
- Lactose / Fructose Breath Test — Carbohydrate malabsorption (lactose intolerance, fructose malabsorption) is extremely common and easily treatable with dietary modification. Consider if bloating worsens after dairy or fruit/honey.
- Fasting Insulin / HOMA-IR — Insulin resistance is linked to gut motility dysfunction and MASLD — both of which can cause bloating. Consider if metabolic risk factors present.
Common causes.
- Irritable Bowel Syndrome (IBS) — Bloating with altered bowel habits (diarrhea, constipation, or mixed), abdominal pain that improves after defecation, no weight loss or blood in stool
- Celiac Disease — Bloating with or without diarrhea, fatigue, iron deficiency anemia — often no classic GI symptoms in adults
- SIBO (Small Intestinal Bacterial Overgrowth) — Severe post-meal bloating, abdominal distension, diarrhea, malabsorption; worsened by fermentable carbohydrates
- Hypothyroidism — Bloating and constipation alongside cold intolerance, fatigue, weight gain, dry skin
- H. pylori Infection — Upper abdominal bloating, early satiety, epigastric discomfort, especially after eating
Diagnostic patterns.
- Elevated tTG-IgA + compatible symptoms — likely Celiac disease. Next step: Refer to gastroenterologist for duodenal biopsy confirmation
- Fecal calprotectin >150 μg/g + diarrhea ± blood — likely Inflammatory bowel disease (IBD). Next step: Gastroenterology referral for colonoscopy
- Elevated TSH + bloating + constipation — likely Hypothyroidism. Next step: Levothyroxine therapy; reassess bowel symptoms after euthyroid state achieved
- Normal all bloods + functional symptoms + Rome IV criteria — likely IBS. Next step: Low-FODMAP diet trial, gut-directed therapy, probiotics
- Post-meal bloating + positive SIBO breath test — likely SIBO. Next step: Rifaximin course + dietary modification; investigate underlying cause
- Positive H. pylori test + upper GI bloating — likely H. pylori infection. Next step: Eradication therapy per ACG 2024 (bismuth quadruple therapy)
Lifestyle.
Non-medical causes
- Rapid eating and air swallowing (aerophagia)
- Carbonated beverage consumption
- High-FODMAP diet (fermentable oligosaccharides, disaccharides, monosaccharides, polyols)
- Constipation (slowed transit causes fermentation and gas buildup)
- Premenstrual water retention (cyclical bloating in women)
- Stress and anxiety (gut-brain axis: slows motility)
- Sedentary lifestyle (impairs gut motility)
- Certain medications: opioids, iron supplements, anticholinergics
Considerations
- Trial low-FODMAP diet for 4-6 weeks with dietitian guidance
- Eat slowly, chew food thoroughly, avoid talking while eating (reduces aerophagia)
- Limit carbonated drinks, straws, and chewing gum
- Regular physical activity improves gut motility
- Stress management: gut-brain axis is well-established; anxiety worsens gut symptoms
- Food and symptom diary to identify trigger foods
- Peppermint oil capsules (enteric-coated): evidence-based for IBS-related bloating
FAQs.
What blood tests should I get for chronic bloating?
Start with: tTG-IgA + total IgA (to screen for celiac disease), TSH (hypothyroidism slows gut motility), CBC (for anemia), and a CMP. If you have diarrhea or concerns about IBD, a fecal calprotectin stool test is the key discriminating test. If upper abdominal bloating is prominent, test for H. pylori with a stool antigen or urea breath test.
Can celiac disease cause bloating without diarrhea?
Yes — this is very common in adults. Over half of adults with celiac disease present with extraintestinal or non-diarrhea symptoms. Bloating may be the only GI complaint. This is why tTG-IgA testing is recommended in adults with IBS-like symptoms, not just those with classic diarrhea.
How is IBS different from IBD when both cause bloating?
The key differentiating test is fecal calprotectin. In IBS, calprotectin is normal (<50 μg/g) because there is no actual inflammation in the gut. In IBD, calprotectin is elevated (>150 μg/g) reflecting active mucosal inflammation. Blood tests (CRP, CBC) are also typically normal in IBS and abnormal in active IBD. Rectal bleeding and nocturnal symptoms strongly favour IBD over IBS.
What is SIBO and how would I know if I have it?
SIBO (small intestinal bacterial overgrowth) occurs when bacteria that normally live in the colon migrate up and colonise the small intestine, fermenting carbohydrates and producing excessive gas. Key symptoms: severe post-meal bloating, abdominal distension that worsens after eating fermentable foods (onions, garlic, legumes, wheat, apples). Diagnosis uses a hydrogen-methane breath test. Treatment includes rifaximin (an antibiotic targeting gut bacteria) and dietary modification.