How to Check for Celiac Disease in Iron Deficiency Anemia
Start with serum IgA anti-tissue transglutaminase (TG2-IgA) antibody testing combined with total IgA level measurement, followed by upper endoscopy with duodenal biopsies if serology is positive. 1
Initial Serological Testing
Begin with TG2-IgA antibody testing as your primary screening tool. This is the most reliable and accurate test for diagnosing active celiac disease 1. When ordering serology:
- Always measure total IgA levels simultaneously to avoid missing IgA-deficient patients who will falsely test negative on IgA-based tests 1
- If IgA deficiency is present (occurs in ~2-3% of celiac patients), order IgG-based tests: IgG deamidated gliadin antibody and TG2-IgG 1
- Note that IgG isotype testing is not specific in the absence of IgA deficiency 1
Interpreting Serological Results
Strongly positive TG2-IgA (>10x upper normal limit) combined with positive endomysial antibody (EMA) in a second blood sample has virtually 100% positive predictive value for celiac disease 1. However, in adults, you should still proceed to endoscopy for differential diagnosis purposes.
Endoscopic Evaluation with Duodenal Biopsies
All adults with positive serology require upper endoscopy with duodenal biopsies before diagnosis 1, 2. This is critical because:
- Alternative diagnoses may be present and can be serious in adults
- Not all commercial TG2-IgA kits are high quality
- Initial biopsy is essential for follow-up, especially in non-responsive patients 2
Biopsy Technique
Take at least 4-6 biopsies from:
- The second portion of the duodenum (distal duodenum)
- The duodenal bulb (to maximize diagnostic yield) 2
The threshold for abnormal intraepithelial lymphocytes (IELs) is ≥25/100 enterocytes, but villous atrophy is required for definite diagnosis 2. Lesser degrees of damage (≥25 IELs without villous atrophy) combined with positive serology may represent "probable celiac disease" 2.
Critical Pitfall: Gluten Avoidance Before Testing
Do not allow patients to reduce or avoid gluten before diagnostic testing as this reduces sensitivity of both serology and biopsy 1. If a patient has already started a gluten-free diet, have them resume normal diet with three slices of wheat bread daily for 1-3 months before repeat testing 1.
Prevalence Context in Iron Deficiency Anemia
Studies show celiac disease prevalence in patients with unexplained iron deficiency anemia ranges from 7-10% 3, 4, making screening highly worthwhile. This is particularly important in:
- Premenopausal women (85.7% of celiac patients with IDA in one study) 3
- Patients with anemia refractory to oral iron treatment 3
- Patients without gastrointestinal symptoms (celiac disease was found even in asymptomatic IDA patients) 5, 4
When to Consider HLA-DQ2/DQ8 Testing
Reserve HLA-DQ2/DQ8 testing for second-line evaluation only 1:
- When diagnosis is doubtful due to inconclusive antibodies or histology
- In patients who started a gluten-free diet before diagnosis
- To rule out celiac disease in seronegative patients with histologic changes (high negative predictive value)
HLA testing has no additional diagnostic value in cases with high TG2-IgA antibodies 1.
Confirmatory Testing
If celiac disease is first identified on intestinal biopsies, perform celiac-specific serology as confirmatory testing before initiating a gluten-free diet 1. If celiac disease is strongly suspected despite negative biopsies, still perform TG2-IgA testing—if positive, consider repeat biopsies 1.