Interpretation of Tissue Transglutaminase IgA Level of 349
A tissue transglutaminase (tTG) IgA level of 349 strongly indicates celiac disease and requires further diagnostic evaluation and management. 1, 2
Diagnostic Significance
- tTG IgA is the recommended initial screening test for celiac disease with high sensitivity (90-96%) in adults 3, 2
- A level of 349 is significantly elevated above normal thresholds (typically 15-20 U/mL depending on the assay) and suggests active celiac disease 1, 3
- Elevated tTG IgA levels correlate strongly with intestinal damage, particularly when >10 times the upper limit of normal 2
- This high level has excellent positive predictive value (>98%) for celiac disease when using standard thresholds 1, 4
Next Steps in Evaluation
- Confirm that testing was performed while on a gluten-containing diet to avoid false negative results 3, 2
- Measure total IgA levels to rule out IgA deficiency which could affect interpretation 1
- Consider additional serologic testing with endomysial antibody (EMA) which has higher specificity (99.6%) 1, 2
- Refer for upper endoscopy with small bowel biopsy (at least 6 specimens from second part of duodenum) as the gold standard for diagnosis 1, 2
- Test for HLA-DQ2/DQ8 haplotypes which are present in almost all celiac disease patients 1
Management Implications
- If celiac disease is confirmed by biopsy, initiate a strict gluten-free diet under the guidance of a dietitian experienced in celiac disease management 3, 2
- Monitor response to diet with follow-up tTG IgA testing at 3-6 months 1, 3
- Be aware that tTG IgA levels typically decline within months of starting a gluten-free diet, with most significant drops occurring in the first year 1, 5
- Persistently elevated tTG IgA levels despite dietary treatment suggest ongoing gluten exposure or poor dietary compliance 1, 3
Important Considerations
- Different tTG IgA assays may have varying sensitivities and specificities; chemiluminescence immunoassays (CLIA) appear more sensitive than fluorochrome-enzyme immunoassays (FEIA) for detecting suboptimal treatment response 5
- False positives can occur in autoimmune liver disease, inflammatory bowel disease, and other autoimmune conditions, so biopsy confirmation is essential 1, 4
- Negative tTG IgA levels after treatment do not guarantee complete mucosal recovery; up to 59% of patients with villous atrophy may have normal tTG IgA levels 6
- Evaluate for common complications including malabsorption, nutritional deficiencies, and associated autoimmune conditions such as type 1 diabetes and thyroid disease 2
Follow-up Protocol
- After initiating gluten-free diet, monitor tTG IgA levels every 3-6 months initially, then annually 1, 3
- Consider follow-up biopsy in 1-3 years to confirm mucosal healing, especially in patients with severe initial presentation 1
- Provide ongoing nutritional assessment and support to ensure adequate intake of essential nutrients that may be deficient in a gluten-free diet 3, 2