Order tissue transglutaminase IgA (tTG-IgA) test (Answer: B)
For an 18-month-old child with normal growth and weight who has a first-degree relative with celiac disease, serologic screening with tTG-IgA is the most appropriate next step. First-degree relatives have a 10-15% lifetime risk of developing celiac disease, making this child a high-risk individual who warrants testing even in the absence of symptoms 1.
Rationale for Testing in Asymptomatic First-Degree Relatives
Current guidelines specifically identify first-degree relatives of patients with celiac disease as a high-risk group requiring screening. 2, 3
- The North American Society for Pediatric Gastroenterology, Hepatology and Nutrition (NASPGHAN) recommends testing asymptomatic individuals with first-degree relatives who have celiac disease 3
- The American Gastroenterological Association identifies first-degree relatives as a population warranting serologic screening 2
- Testing should be performed using IgA tissue transglutaminase (tTG-IgA) antibodies with documentation of normal total serum IgA levels 1
Why Not Reassurance Alone
While normal growth and weight are reassuring signs that make active celiac disease unlikely at this moment 1, simply reassuring the parents without testing misses the opportunity to identify early or subclinical disease in a high-risk individual.
- Celiac disease can present with a variety of phenotypes including subclinical and potential forms where patients have minimal or no symptoms 4
- The disease can occur at any age with multifaceted clinical presentations 4
- Early detection allows for timely intervention before complications develop, such as osteoporosis, anemia, and growth failure 5
Why Not Start a Gluten-Free Diet
Starting a gluten-free diet without diagnostic confirmation is inappropriate and potentially harmful. 2
- Diagnostic tests must be performed before initiating gluten restriction, as positive serologic results may resolve and histologic findings may improve with gluten removal 2
- Initiating a gluten-free diet without biopsy confirmation can lead to diagnostic uncertainty and make future testing unreliable 2
- The psychosocial burden of an unnecessary lifelong gluten-free diet is significant 5
Diagnostic Approach
The recommended testing strategy is straightforward:
- Initial screening with IgA tTG-IgA combined with total IgA measurement 2
- The IgA tTG-IgA has sensitivity of 90-96% and specificity greater than 95% 2
- If tTG-IgA is positive, referral to a pediatric gastroenterologist for intestinal biopsy is indicated 3
- In cases of IgA deficiency, IgG-based tests (IgG tTG-IgA or IgG EMA) should be used 2
Important Caveats
Parents should be educated about symptoms that would warrant immediate testing if they develop:
- Poor weight gain or growth failure 1
- Unexplained irritability or behavioral changes 1
- Gastrointestinal symptoms including chronic diarrhea, abdominal pain, or bloating 3
- If the child develops type 1 diabetes in the future, immediate screening would be indicated 1
The child should remain on a gluten-containing diet until testing is complete to avoid false-negative results 2.