Order tissue transglutaminase IgA (tTG-IgA) test
The most appropriate next step is to order a tTG-IgA test combined with total IgA measurement, as first-degree relatives of celiac disease patients have a 10-15% lifetime risk and warrant serologic screening even when asymptomatic. 1, 2, 3
Why Screening Is Indicated
- First-degree relatives represent a high-risk population specifically identified by the American Gastroenterological Association as requiring screening, regardless of symptoms 2, 3
- The 10-15% lifetime risk in siblings is substantially elevated compared to the general population prevalence of approximately 1% 1, 4, 5
- Early detection allows intervention before complications develop, including malabsorption, nutritional deficiencies, osteoporosis, and associated autoimmune conditions 2, 5
Recommended Testing Strategy
- Initial test: IgA tissue transglutaminase (tTG-IgA) combined with total IgA measurement 2, 3, 6
- This combination has sensitivity of 90-96% and specificity greater than 95% 2, 3
- Total IgA measurement is essential because selective IgA deficiency occurs in 1-3% of celiac disease patients and would cause false-negative tTG-IgA results 2, 7
- If IgA deficiency is detected, switch to IgG-based tests (IgG tTG or IgG EMA) 2, 3, 7
Critical Pre-Testing Requirement
The child must remain on a gluten-containing diet until all testing is complete 2, 3. Never start a gluten-free diet before diagnostic workup, as this leads to false-negative serology and would require a prolonged gluten challenge (at least three slices of wheat bread daily for 1-3 months) to re-establish the diagnosis 2.
Why Reassurance Alone Is Inadequate
- Current guidelines do not support simply reassuring parents without screening when a first-degree relative has celiac disease 2
- The child appears healthy now, but celiac disease can be subclinical and still cause long-term complications 4, 5
- Many children with celiac disease are asymptomatic at diagnosis, particularly when identified through screening of at-risk groups 6
Why Starting a Gluten-Free Diet Is Inappropriate
- A gluten-free diet should never be initiated without diagnostic confirmation, as it represents a significant lifelong dietary burden 2, 6
- Starting the diet prematurely makes future diagnostic testing unreliable and potentially requires a prolonged gluten challenge 2
- Biopsy confirmation is recommended, especially in asymptomatic children, before prescribing significant dietary changes 8, 6
Follow-Up Based on Test Results
If tTG-IgA is positive: Proceed to upper endoscopy with duodenal biopsy (at least 4-6 specimens from the second part of the duodenum or beyond) for histological confirmation 8, 2, 6
If tTG-IgA is negative: Educate parents about symptoms warranting immediate retesting, including poor weight gain or growth failure, unexplained irritability or behavioral changes, chronic diarrhea, abdominal pain, or constipation 2, 3
Common Pitfall to Avoid
The most critical error would be starting a gluten-free diet based solely on family history without serologic or histologic confirmation 2. This creates diagnostic uncertainty that can persist for years and may require an uncomfortable gluten challenge to resolve 8.