Endomysial Antibody IgA (EMA-IgA) Test
Endomysial antibody IgA (EMA-IgA) is a highly specific serologic test for celiac disease that detects antibodies against tissue-bound transglutaminase-2 in the connective tissue surrounding smooth muscle fibers, serving primarily as a confirmatory test rather than initial screening.
Test Methodology and Technical Characteristics
EMA-IgA is detected using indirect immunofluorescence on primate esophagus or human umbilical cord tissue sections, making it more labor-intensive and dependent on operator experience compared to automated ELISA-based tests 1
The test identifies antibody reactivity to tissue-bound transglutaminase-2 (TG-2), which is the same autoantigen detected by tissue transglutaminase antibody tests but in its native tissue form 1
EMA testing requires specialized technical expertise and subjective interpretation of fluorescence patterns, which limits its use for high-throughput screening 1
Diagnostic Performance
EMA-IgA demonstrates exceptional specificity of 99.6% in adults and 93.8% in children, making false-positive results extremely rare 2, 3
The sensitivity is 100% in untreated celiac disease patients with subtotal villous atrophy, though it drops to approximately 45-47% in patients already following a gluten-free diet 4, 5
When combined with tissue transglutaminase IgA (tTG-IgA) levels exceeding 10 times the upper limit of normal, the positive predictive value for celiac disease approaches virtually 100% 1, 2
Clinical Role in Diagnostic Algorithm
EMA-IgA is best suited for second-line confirmatory testing after an initial positive tTG-IgA result, rather than as a first-line screening test 1
The American Gastroenterological Association recommends tTG-IgA as the preferred initial screening test due to its automation capability and convenience, reserving EMA for confirmation 1, 6
The superior specificity of EMA makes it particularly valuable when diagnostic certainty is needed before proceeding to endoscopy, especially in patients with borderline tTG-IgA elevations 1
Monitoring Treatment Response
EMA-IgA titers decline during adherence to a gluten-free diet, with antibodies becoming undetectable in most compliant patients over time 7
However, EMA-IgA has limited sensitivity (45%) for detecting persistent villous atrophy in patients on a gluten-free diet, meaning a negative result does not exclude ongoing intestinal damage 5
The test should not be relied upon as the sole marker of mucosal healing, as approximately half of patients with persistent villous atrophy will have negative EMA results 5
Critical Testing Requirements
Patients must be consuming adequate gluten (at least 10g daily) at the time of testing to avoid false-negative results 2, 3
Total IgA levels must be measured concurrently, as selective IgA deficiency occurs in 1-3% of celiac disease patients and causes falsely negative IgA-based antibody tests 1, 6
In IgA-deficient patients, IgG-based tests (such as IgG deamidated gliadin peptide or IgG tissue transglutaminase) should be used instead 1
Practical Limitations
The labor-intensive nature and requirement for experienced interpretation make EMA less practical than automated tTG-IgA assays for routine screening 1
Point-of-care versions of antibody tests exist but may present quality control difficulties when used by inexperienced operators 1
The test's high specificity means that a positive EMA result strongly supports the diagnosis, but the workflow inefficiency limits its use as a primary screening tool in low-prevalence populations 1