From the Guidelines
To diagnose celiac disease, the initial test should be a celiac serology panel while the patient is still consuming gluten, including tissue transglutaminase antibodies (tTG-IgA), total serum IgA, and sometimes endomysial antibodies (EMA-IgA) and deamidated gliadin peptide antibodies (DGP-IgG and IgA) 1.
Key Tests for Diagnosis
- Total serum IgA to check for IgA deficiency, which is more common in celiac patients and could lead to false-negative results on IgA-based tests 1
- IgA anti-tissue transglutaminase (TTG) antibody, the preferred test in persons older than two years 1
- IgG- and IgA-deamidated gliadin peptides, especially in younger children to improve sensitivity 1
- Endomysial antibodies (EMA-IgA) for additional confirmation
Importance of Gluten Consumption Before Testing
It's crucial that patients continue to consume gluten (equivalent to at least 1-2 slices of bread daily) for 6-8 weeks before testing, as eliminating gluten can lead to false-negative results 1.
Confirmation and Further Testing
If serologic tests are positive, the diagnosis should be confirmed with an upper endoscopy with multiple duodenal biopsies 1. Genetic testing for HLA-DQ2 and HLA-DQ8 can be helpful in certain situations, particularly to rule out celiac disease in patients already on a gluten-free diet or with equivocal results 1. For patients already on a gluten-free diet who cannot or will not resume gluten consumption, HLA typing followed by a gluten challenge and biopsy may be necessary for accurate diagnosis 1.
From the Research
Tests for Celiac Disease
To diagnose celiac disease, several tests can be ordered, including:
- Immunoglobulin A (IgA) tissue transglutaminase antibody (tTG) test, which is the preferred initial test 2
- IgA endomysial antibody (EMA) test, which can be used to confirm the diagnosis 3, 4
- Total serum IgA level, which should be measured to exclude selective IgA deficiency and avoid false-negative test results 2
- Human leukocyte antigens DQ2 and DQ8 testing, which can help exclude the diagnosis 2
- IgG antibodies against deamidated gliadin peptides (DGP), which can be used in combination with IgA anti-tTG antibodies for diagnosis 5
Interpretation of Test Results
When interpreting test results, the following should be considered:
- A positive IgA tTG test result does not necessarily confirm the diagnosis, as it can have a low positive predictive value 3
- A normal tTG level does not predict recovery of villous atrophy in patients with celiac disease on a gluten-free diet 3
- The combination of IgG anti-DGP and IgA anti-tTG antibodies can show high sensitivity and specificity for diagnosis 5
- Patients with positive serologic test results should be referred to a gastroenterologist for endoscopic small intestinal biopsies to confirm the diagnosis 2
Diagnostic Approach
The diagnostic approach for celiac disease may involve a 2-step approach, using tTG first and then EMA, which can provide high sensitivity and specificity 3 The use of nondeamidated IgA/IgG gliadin antibodies may not confer additional diagnostic benefit 3 A gluten-free diet should not be started before confirming the diagnosis of celiac disease 2