Gut Health Tests Explained: Which Tests Actually Work and Which Are a Waste of Money
Gut Health Tests Explained: Which Tests Actually Work and Which Are a Waste of Money
By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist and founder of Casa de Sante
Key Takeaways
- Not all gut health tests are created equal — some have strong clinical evidence, others are essentially expensive guesswork
- Evidence-based tests: hydrogen/methane breath tests (SIBO), celiac serology, stool calprotectin, colonoscopy with biopsy
- Limited evidence: commercial microbiome stool tests (Viome, GI-MAP, etc.) — interesting for research, but actionable clinical recommendations are still evolving
- Food sensitivity IgG panels are NOT recommended by any major medical society — they measure exposure, not intolerance
- The gold standard for food triggers remains the elimination diet (low FODMAP), not blood tests
Evidence-Based Tests
1. Hydrogen/Methane Breath Test (SIBO)
What it tests: Small intestinal bacterial overgrowth
How it works: You drink a sugar solution (lactulose or glucose). If bacteria in the small intestine ferment it, they produce hydrogen and/or methane gas, which is measured in your breath.
Accuracy: Lactulose breath test has ~65-70% sensitivity and 85% specificity. Glucose breath test has higher specificity but lower sensitivity (misses distal SIBO).
When to get it: Bloating within 30-60 minutes of eating, especially if low FODMAP diet only partially helps.
2. Celiac Serology (Blood Test)
What it tests: Celiac disease (autoimmune gluten reaction)
Tests include: tTG-IgA (tissue transglutaminase antibody), total IgA, and sometimes DGP (deamidated gliadin peptide).
Accuracy: tTG-IgA has 95-98% sensitivity and specificity. Excellent screening test.
Important: You must be eating gluten for 6+ weeks before the test. Going gluten-free before testing produces false negatives.
3. Stool Calprotectin
What it tests: Intestinal inflammation (distinguishes IBS from IBD)
How it works: Calprotectin is a protein released by neutrophils (white blood cells) during inflammation. Elevated stool calprotectin strongly suggests inflammatory bowel disease (Crohn's or ulcerative colitis) rather than IBS.
Accuracy: Sensitivity >90% for IBD. A normal calprotectin makes IBD very unlikely.
When to get it: Persistent diarrhea, blood in stool, unexplained weight loss, or IBS symptoms that do not respond to typical treatment.
4. Lactose Breath Test
What it tests: Lactose malabsorption
How it works: Drink lactose solution, measure breath hydrogen. High hydrogen = undigested lactose being fermented by bacteria.
Alternative: A 2-week lactose elimination trial is equally diagnostic and free.
5. Colonoscopy
What it tests: Structural abnormalities, IBD, polyps, cancer
When needed: Age 45+ (standard screening), alarm symptoms (blood in stool, unintended weight loss, family history of colon cancer, new symptoms after age 50), or IBS symptoms not responding to treatment.
Tests with Limited Clinical Utility
Commercial Microbiome Tests (Viome, Thryve, GI-MAP, etc.)
These tests sequence the DNA of bacteria in your stool and provide a report on your microbiome composition. The science of microbiome analysis is real and important for research. The problem: we do not yet have enough evidence to translate a specific microbiome profile into specific clinical recommendations.
IgG Food Sensitivity Panels
These blood tests measure IgG antibodies to specific foods. The American Academy of Allergy, Asthma & Immunology, the European Academy of Allergy and Clinical Immunology, and the Canadian Society of Allergy and Clinical Immunology ALL recommend against using IgG testing for food intolerance. IgG indicates exposure to a food, not intolerance. Everyone who eats eggs will have IgG antibodies to egg — it does not mean they are intolerant.
The Best "Test" for IBS
The low FODMAP elimination diet, guided by a FODMAP-trained dietitian, remains the gold standard for identifying IBS food triggers. It is more accurate, more actionable, and more cost-effective than any blood test for food triggers.
🛒 Support During Testing and Elimination
- Digestive Enzymes — During the FODMAP reintroduction phase, enzymes provide a safety net. They break down FODMAPs you are testing, reducing severity of reactions during food challenges.
- FODMAP Enzymes + Probiotics — Microbiome support during dietary elimination when your fiber and prebiotic intake is naturally reduced
Medical Disclaimer: This article is for educational purposes only. Diagnostic testing should be ordered and interpreted by your healthcare provider. Dr. Adegbola is the founder of Casa de Sante.
