Getting Diagnosed with Celiac Disease
Celiac disease is diagnosed through a specific sequence of medical tests. Understanding this process helps you navigate the diagnostic workup efficiently and avoid the most common mistake that delays diagnosis — going gluten-free before testing.
Step 1: Serological Blood Tests
Blood testing is the first step in evaluating for celiac disease. The standard celiac panel includes:
Tissue Transglutaminase IgA (tTG-IgA)
This is the most accurate single blood test for celiac disease, with sensitivity and specificity both over 95% in patients who are not IgA deficient. Tissue transglutaminase is the enzyme that modifies gluten peptides in the intestine; people with celiac disease develop antibodies against it.
A positive tTG-IgA in someone eating a gluten-containing diet is highly indicative of celiac disease and warrants follow-up intestinal biopsy.
Total IgA
This must be measured alongside tTG-IgA because IgA deficiency (affecting 1 in 500 people) will cause a false negative on all IgA-based tests. If IgA deficiency is found, IgG-based tests (tTG-IgG, DGP-IgG) are used instead.
Deamidated Gliadin Peptide Antibodies (DGP-IgA and DGP-IgG)
Particularly useful in young children (under 2 years) and IgA-deficient individuals. Less specific than tTG-IgA in older children and adults.
Endomysial Antibody (EMA-IgA)
Highly specific for celiac disease (very few false positives) but less sensitive than tTG-IgA. Often used to confirm a positive tTG result.
What the Numbers Mean
Blood test results come as "positive," "negative," or in some labs with numerical values compared to a reference range. A positive result means antibodies were detected above the threshold. The level of elevation can sometimes indicate the severity of intestinal damage — very high tTG levels correlate with more extensive villous atrophy.
Critical rule: Do not start a gluten-free diet before these tests. If you're already eating GF, the tests will likely be negative even if you have celiac disease, because the immune response quiets without gluten exposure. You would then need to do a formal "gluten challenge" (eating gluten for 6-8 weeks) before re-testing — an unpleasant process.
Step 2: Intestinal Biopsy (Endoscopy)
A positive celiac serology test requires confirmation with an intestinal biopsy. This is performed during an upper endoscopy (EGD — esophagogastroduodenoscopy), in which a gastroenterologist passes a flexible camera through the mouth into the small intestine.
During the procedure, which takes 15-20 minutes and is done under sedation, the doctor takes multiple small tissue samples from the duodenum (first part of the small intestine, the primary site of celiac damage).
What the Biopsy Looks For
The pathologist examines the biopsy samples for:
- Villous atrophy — shortening or flattening of intestinal villi
- Crypt hyperplasia — deepening of the crypts (the base of villi) as the intestine tries to compensate
- Intraepithelial lymphocytes (IEL) — increased immune cells within the intestinal lining
The Marsh Classification
Celiac disease biopsy findings are graded using the Marsh classification (or modified Marsh-Oberhuber classification):
- Marsh 0 — Normal intestine
- Marsh 1 — Increased intraepithelial lymphocytes only (>25 per 100 epithelial cells)
- Marsh 2 — IEL increase + crypt hyperplasia
- Marsh 3a — Partial villous atrophy
- Marsh 3b — Subtotal villous atrophy
- Marsh 3c — Total villous atrophy
Marsh 3a-3c are diagnostic of celiac disease when combined with positive serology. Marsh 1-2 are considered "potential celiac" — the person has the genetic predisposition and early immune activity but not full villous atrophy. These cases require monitoring.
How Many Biopsies?
Current guidelines recommend taking at least 4-6 biopsy samples, including at least 1 from the duodenal bulb (the first portion of the duodenum), where early celiac disease may be most apparent. Patchy damage is common, so multiple samples are essential to avoid missing the diagnosis.
Step 3: Genetic Testing (HLA-DQ2/DQ8)
Genetic testing for the HLA-DQ2 and HLA-DQ8 variants is not used to diagnose celiac disease, but it's valuable in specific situations:
- When someone is already on a GF diet and can't/won't return to eating gluten for re-testing — a negative genetic test effectively rules out celiac disease, while a positive indicates risk but not diagnosis
- Screening first-degree relatives — a negative result means they will never develop celiac disease and don't need monitoring
- When biopsy and serology give conflicting results — genetic testing provides important context
- Evaluating potential celiac disease (Marsh 1-2) — positive HLA supports the diagnosis
About 30-40% of the general population carries HLA-DQ2 or DQ8, but only about 1% develops celiac disease, so a positive genetic test alone does not mean someone has or will get celiac disease.
Diagnosing Celiac When Already Gluten-Free
This is a challenging situation. Options include:
- Gluten challenge: Eat regular amounts of gluten for 6-8 weeks, then repeat serology and biopsy. This allows accurate diagnosis but may cause significant symptoms in people who react strongly.
- Shorter challenge: Some protocols use 2 slices of wheat bread daily for 2 weeks before testing — more tolerable than a full 6-week challenge, though may produce borderline rather than clearly positive results.
- Genetic testing first: If HLA-DQ2 and DQ8 are both negative, celiac disease can be ruled out without a gluten challenge.
- Clinical assessment: In some cases (positive family history, known associated autoimmune condition, history of strong symptoms when consuming gluten), a physician may diagnose based on the overall clinical picture.
- tTG-IgA more than 10x the upper limit of normal
- Positive EMA-IgA on a separate blood sample
- Positive HLA-DQ2 or DQ8
- Symptoms consistent with celiac disease
- Skin biopsy of unaffected skin near a blister, showing IgA deposits — this is the gold standard
- Blood test results may be less strongly positive than in intestinal celiac
- Intestinal biopsy in DH often shows celiac changes but may be less severe
- Begin a strict gluten-free diet immediately — this is the only treatment
- Baseline nutrient testing — iron, ferritin, folate, B12, vitamin D, calcium, zinc
- DEXA bone density scan — at diagnosis and periodically to monitor for osteoporosis
- Referral to a registered dietitian experienced in celiac disease management
- Screening family members — first-degree relatives should be tested
- Follow-up testing — tTG-IgA 6-12 months after starting GF diet to confirm antibody normalization; repeat biopsy in cases of ongoing symptoms or persistent positive serology
Diagnosing Celiac Disease in Children
The European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) guidelines allow for diagnosis without biopsy in children with:
This approach (sometimes called the "no-biopsy" pathway) spares children the endoscopy procedure while maintaining diagnostic accuracy. It's increasingly used in pediatric practice but not yet standard in the US.
Dermatitis Herpetiformis Diagnosis
DH (the skin manifestation of celiac disease) is diagnosed differently from intestinal celiac:
After Diagnosis: What Happens Next
Once celiac disease is confirmed: