What labs should be ordered for a child with weight loss and refusal of solid foods to evaluate anemia, iron deficiency, celiac disease, eosinophilic esophagitis, and micronutrient deficiencies?

Laboratory Evaluation for Child with Weight Loss and Solid Food Refusal

Order a comprehensive panel including: complete blood count (CBC), serum ferritin, tissue transglutaminase IgA (TG2-IgA) with total IgA, vitamin D (25-OH), folate, vitamin B12, and calcium to screen for anemia, iron deficiency, celiac disease, and micronutrient deficiencies. Eosinophilic esophagitis cannot be diagnosed by bloodwork and requires endoscopy with esophageal biopsies 1.

Core Laboratory Tests

For Anemia and Iron Deficiency

• CBC with hemoglobin and mean corpuscular volume (MCV): Iron deficiency anemia presents with low hemoglobin and low MCV only at end-stage deficiency 2
• Serum ferritin: The single most important test for iron deficiency
  • Use threshold <12 μg/L for children under 5 years
  • Use threshold <15 μg/L for children over 5 years
  • If inflammation suspected, use higher threshold of 30 μg/L 2
• C-reactive protein (CRP): Order alongside ferritin to detect concurrent inflammation that may falsely elevate ferritin 2

Iron deficiency is common in celiac disease, affecting 28% at diagnosis with 9% having frank anemia 3. However, iron parameters (serum iron, TIBC, transferrin saturation) add little diagnostic value beyond ferritin 2.

For Celiac Disease

• Tissue transglutaminase IgA (TG2-IgA): Primary screening test
• Total IgA level: Essential to identify IgA deficiency, which occurs in celiac disease and would cause false-negative TG2-IgA 4

Critical caveat: Do not start a gluten-free diet before obtaining these antibodies, as this will cause false-negative results 4. High TG2-IgA levels (>10x upper limit of normal) in children may allow biopsy-avoiding diagnosis in select cases, but this requires gastroenterology consultation 4.

For Micronutrient Deficiencies

• Vitamin D (25-OH): Most commonly deficient vitamin in celiac disease, affecting 70% of children at diagnosis and remaining low even after 6 months of gluten-free diet 5
• Folate: Deficient in 14% at celiac diagnosis 3
• Vitamin B12: Rarely deficient (1% at diagnosis) but should be checked 3
• Calcium: Hypocalcemia is uncommon but should be assessed 3

What NOT to Order

Do not order thyroid function tests (TSH, free T4) routinely. Despite common practice, thyroid dysfunction is not found at diagnosis or follow-up in celiac disease patients 3. Only order if specific thyroid symptoms are present.

Do not order eosinophil count or IgE levels for eosinophilic esophagitis screening—these are not diagnostic. EoE requires endoscopy with esophageal biopsies showing ≥15 eosinophils per high-power field 1.

Clinical Algorithm

1. If celiac antibodies are positive: Refer to pediatric gastroenterology for endoscopy with duodenal biopsies before starting gluten-free diet 4

2. If iron deficiency confirmed: Initiate oral iron supplementation while investigating underlying cause 6

3. If symptoms persist despite negative celiac serology and treated iron deficiency: Consider endoscopy to evaluate for eosinophilic esophagitis, especially if:

   • Child refuses solid foods or has dysphagia
   • Symptoms mimic reflux but don't respond to proton pump inhibitors
   • Personal or family history of atopy 1

4. If vitamin D deficiency found: Supplement regardless of other diagnoses, as this is highly prevalent and persists even with dietary intervention 5

Important Pitfalls

• Don't wait for anemia to diagnose iron deficiency: Ferritin drops first; anemia is a late finding 2
• Don't interpret normal ferritin as excluding iron deficiency if inflammation present: Ferritin is an acute phase reactant; check CRP concurrently 2
• Don't assume gluten-free diet alone corrects all deficiencies: Iron deficiency persists in 8% and vitamin D deficiency in 25% of celiac patients on gluten-free diet 3
• Don't order extensive micronutrient panels at follow-up: After initial diagnosis and treatment, only recheck on clinical indication (fatigue, poor growth) rather than routinely 3

The combination of weight loss and solid food refusal in a child warrants this comprehensive initial evaluation, as celiac disease can present with feeding difficulties that overlap with eosinophilic esophagitis 7, 8. Up to 6% of celiac patients have concurrent EoE 7.