Which blood tests should be obtained for children with avoidant/restrictive food intake disorder (ARFID) to screen for anemia, nutrient deficiencies, electrolyte disturbances, and organ dysfunction, and why?

Blood Work for Children with ARFID

Children with ARFID require screening for anemia (CBC with indices), iron deficiency (ferritin, transferrin saturation), and key micronutrient deficiencies (vitamins B1, B2, B12, C, K, zinc, potassium) because their restricted dietary patterns create high risk for multiple nutritional deficiencies that can impair growth and neurodevelopment.

Core Laboratory Panel

Complete Blood Count with Indices

• Obtain CBC with MCV, RDW, and reticulocyte count as the foundation of your workup 1
• MCV classifies anemia as microcytic, normocytic, or macrocytic and guides further testing 1
• RDW >14% with low MCV indicates iron deficiency anemia, while RDW ≤14% with low MCV suggests thalassemia 1
• Reticulocyte count distinguishes decreased bone marrow production from increased destruction or blood loss 1

Iron Studies

• Measure serum ferritin to assess iron stores; levels <30 μg/L indicate iron deficiency in the absence of inflammation 1
• Check transferrin saturation to evaluate functional iron availability 1
• Obtain CRP to identify inflammation that may falsely elevate ferritin (ferritin up to 100 μg/L may still indicate iron deficiency when inflammation is present) 1
• Children with ARFID show significantly lower iron intake compared to healthy controls, making iron deficiency highly prevalent 2

Micronutrient Assessment

• Screen for vitamins B1, B2, B12, C, and K because ARFID patients meet only 20-30% of recommended intake for most vitamins 2
• Measure zinc and potassium levels, as these are significantly lower in ARFID versus controls 2
• Vitamin K and B12 deficiencies correlate with limited vegetable and protein intake characteristic of ARFID 3

Why These Tests Matter

Macronutrient Deficiencies Drive Micronutrient Risk

• ARFID patients consume significantly lower total energy, protein, fat, and carbohydrates compared to healthy peers 2
• Their diet is high in processed foods, total carbohydrates, and added sugars, but low in vegetables and protein 3
• Vegetable and protein intake are significantly reduced, directly causing deficiencies in vitamins K, B12, iron, and zinc 3

Anemia Screening Is Essential

• Children aged 9-18 months are at highest risk for iron deficiency anemia due to rapid growth and inadequate dietary iron 1
• Screen all ARFID patients for anemia with hemoglobin; levels <11.0 g/dL in children aged 1-5 years meet diagnostic criteria 1, 4
• Confirm positive screening with repeat hemoglobin or hematocrit before initiating treatment 5, 4

Electrolyte Monitoring for Refeeding Risk

• In severely malnourished ARFID patients, phosphorus and magnesium supplementation may prevent refeeding syndrome during nutritional rehabilitation 6
• Electrolyte imbalances can occur with aggressive refeeding, though more aggressive protocols appear well-tolerated in most cases 6

Age-Specific Screening Recommendations

High-Risk Populations (Screen Universally)

• Screen all ARFID patients between ages 9-12 months, again at 15-18 months, then annually from ages 2-5 years 5
• Children with limited food variety or amount are at particularly high risk for multiple deficiencies 2

Risk Factors Requiring Screening

• Excessive cow's milk intake (>24 oz daily) 5
• Limited iron-fortified foods in diet 5
• History of prematurity or low birth weight 5
• Introduction of cow's milk before age 12 months 5
• Restricted diets or limited dietary variety (hallmark of ARFID) 2, 3

Critical Pitfalls to Avoid

• Do not delay presumptive iron treatment in children with microcytic anemia and clear ARFID risk factors while waiting for ferritin results 1
• Do not overlook that ARFID patients often report no fruits or vegetables in their top five food categories, making multiple micronutrient deficiencies likely 3
• Do not assume normal hemoglobin rules out other micronutrient deficiencies; ARFID creates risk for vitamins B1, B2, C, K, zinc, and potassium deficiency independent of anemia 2
• Do not forget that serum ferritin is an acute phase reactant; inflammation can mask iron deficiency even with ferritin up to 100 μg/L 1

Follow-Up Testing

Confirming Iron Deficiency Treatment Response

• Repeat hemoglobin at 4 weeks after starting iron supplementation (3 mg/kg/day between meals) 5, 4
• An increase ≥1 g/dL in hemoglobin or ≥3% in hematocrit confirms iron deficiency anemia 5, 4
• Continue iron therapy for 2-3 additional months to replenish stores even after hemoglobin normalizes 4, 7

Non-Responsive Anemia

• If anemia persists after 4 weeks despite compliance, obtain MCV, RDW, and serum ferritin 5
• Serum ferritin ≤15 μg/L confirms iron deficiency; >15 μg/L suggests alternative diagnosis 7
• Consider hematology referral if workup remains inconclusive 1

Long-Term Consequences of Untreated Deficiencies

• Untreated iron deficiency anemia causes neurodevelopmental delays, decreased motor activity, impaired social interaction, and reduced attention span that may persist beyond school age 4, 7
• Nutritional deficiencies from ARFID increase risk for stunted growth and developmental problems 2, 8
• ARFID prevalence can reach 3% in the general population, making systematic nutrition screening essential at every pediatric visit 8