What is the most appropriate next step for an 18‑month‑old child with normal growth and a first‑degree relative (older sibling) diagnosed with celiac disease?

Screening for Celiac Disease in First-Degree Relatives

Order tissue transglutaminase IgA (tTG-IgA) test now (Option B). This 18-month-old child with a first-degree relative with celiac disease meets clear criteria for screening, regardless of being asymptomatic with normal growth.

Rationale for Screening

First-degree relatives of patients with celiac disease should be offered screening, as explicitly recommended by the American Gastroenterological Association 1, 2. This recommendation applies even when the child is asymptomatic and growing normally, because:

• First-degree relatives have a substantially elevated risk of celiac disease compared to the general population 2
• Early detection prevents long-term complications including growth failure, nutritional deficiencies, and increased risk of autoimmune conditions 1
• The child is at an age where gluten has been introduced into the diet, making serologic testing reliable 2

Appropriate Screening Test

Measure IgA tissue transglutaminase (tTG-IgA) antibodies with documentation of normal total serum IgA levels as the primary screening test 1, 2, 3. This test has:

• Sensitivity of 90-96% and specificity >95% for celiac disease 1, 3
• Superior performance compared to other serologic markers 1

If IgA deficiency is detected, use IgG-based tests (IgG tTG and deamidated gliadin peptide antibodies) instead 1, 2.

Why Not Reassurance Alone

Simply reassuring the parents (Option A) is inappropriate because:

• Normal growth and weight do not exclude celiac disease—many children are asymptomatic at diagnosis 1
• The family history alone justifies screening per established guidelines 1, 2
• Missing the diagnosis could lead to preventable complications over time 1

Why Not Empiric Gluten-Free Diet

Starting a gluten-free diet without testing (Option C) is contraindicated because:

• Diagnostic tests must be performed before initiating gluten restriction, as positive serologic results may resolve and histologic findings may improve with gluten removal 1, 3
• Initiating a gluten-free diet before completing diagnostic testing leads to false-negative results 3
• The burden of a gluten-free diet is significant and should not be imposed without confirmed diagnosis 1

Follow-Up Screening Protocol

If the initial screening is negative:

• Repeat screening within 2 years of the initial test 1, 2, 4
• Screen again 5 years after initial testing 1, 2, 4
• Consider more frequent screening if symptoms develop or if the child develops other autoimmune conditions 1, 2

Role of HLA Typing

Consider HLA-DQ2/DQ8 testing at initial screening to stratify future risk and guide re-screening intervals 2, 3. The absence of both HLA-DQ2 and HLA-DQ8 has >99% negative predictive value and essentially rules out celiac disease, eliminating the need for future screening 2, 3, 5.

If Screening Is Positive

Should the tTG-IgA be elevated:

• Refer to pediatric gastroenterology for duodenal biopsy to confirm diagnosis before dietary changes 1, 2, 3
• Obtain at least 4-6 biopsy specimens from the second part of the duodenum or beyond 2, 3
• Only after biopsy confirmation should a strict gluten-free diet be initiated 1, 2
• Refer to a dietitian experienced in celiac disease management 2, 3

Common Pitfall to Avoid

The most critical error would be starting dietary restriction before obtaining diagnostic testing, as this makes subsequent diagnosis extremely difficult and may require prolonged gluten challenge (1-3 months or longer) to establish the diagnosis 3.