Normal Tissue Transglutaminase IgA Result
A tTG IgA level of <1.02 is negative and effectively rules out celiac disease in patients consuming adequate gluten, indicating no further celiac-specific workup is needed. 1
Interpretation of the Result
This result is well below the diagnostic threshold (typically 4-20 U/mL depending on the assay) and falls within the normal reference range, indicating absence of celiac disease antibodies. 2
The negative tTG IgA has a negative predictive value approaching 100% when the patient has been consuming adequate gluten (at least 10g daily for 6-8 weeks prior to testing). 1, 3
In adults, tTG IgA demonstrates 90.7% sensitivity and 87.4% specificity at standard diagnostic thresholds, making it highly reliable for excluding celiac disease when negative. 4
Clinical Significance
No celiac disease is present based on this serologic result, assuming the patient was consuming a normal gluten-containing diet at the time of testing. 1
This result confirms that IgA-based antibody tests are valid (assuming total IgA was measured and is normal), as the test is functioning properly to detect antibodies if they were present. 1
Approximately 2-10% of patients with actual celiac disease could theoretically have false-negative results, but this occurs primarily in patients who have already reduced gluten intake or have very early/mild disease. 1
Important Caveats
The patient must have been consuming adequate gluten (at least 10g daily for 6-8 weeks) before testing to avoid false-negative results. 1, 5
Total IgA levels should be measured concurrently to rule out selective IgA deficiency (occurs in 1-3% of celiac patients), which would cause falsely negative IgA-based antibody tests. 4, 1
If IgA deficiency is present, IgG-based testing (IgG deamidated gliadin peptide or IgG tTG) must be performed instead, as IgA tests are unreliable in this population. 4, 1
When to Pursue Further Testing Despite Negative Result
Proceed to upper endoscopy with duodenal biopsies if clinical suspicion remains very high despite negative serology (chronic diarrhea, weight loss, malabsorption, family history). 1, 5
Consider HLA-DQ2/DQ8 genetic testing if seronegative celiac disease is suspected—absence of both alleles has >99% negative predictive value and essentially rules out celiac disease. 1, 5
Repeat testing after ensuring adequate gluten consumption if the patient had reduced gluten intake before the initial test. 1
Next Steps
No gluten-free diet should be initiated based on symptoms alone without confirmed celiac disease, as this can lead to nutritional deficiencies and unnecessary dietary restrictions. 1
Consider alternative diagnoses for gastrointestinal symptoms, such as irritable bowel syndrome, inflammatory bowel disease, or non-celiac gluten sensitivity. 1
Repeat celiac screening may be warranted in high-risk populations (type 1 diabetes, first-degree relatives of celiac patients, autoimmune thyroid disease) if new symptoms develop, even with previously negative serology. 4, 1