What are the differential diagnoses and initial work‑up for a child with growth faltering (failure to thrive)?

Growth Faltering: Differential Diagnoses and Initial Work-Up

Primary Differential Diagnoses

Growth faltering most commonly results from inadequate caloric intake due to behavioral or psychosocial factors, but organic causes must be systematically excluded through targeted evaluation based on clinical presentation. 1, 2

Inadequate Caloric Intake (Most Common)

• Behavioral/psychosocial issues including feeding difficulties, incorrect formula preparation, limited food availability, or family food insecurity 2, 3
• Swallowing dysfunction with aspiration (occurs in 79% of certain conditions requiring modified feeding strategies) 1
• Gastroesophageal reflux disease (GERD) presenting with irritability during feeding and vomiting 1

Inadequate Caloric Absorption

• Cystic fibrosis with pancreatic insufficiency (presents with normal birth weight followed by early growth failure, weight faltering before height faltering) 1
• Celiac disease causing malabsorption 1
• Pancreatic insufficiency from other causes including Shwachman-Diamond syndrome (79% present with failure to thrive, 64% with weight below 3rd percentile) 1

Excessive Caloric Expenditure

• Hyperthyroidism causing increased metabolic demands 4
• Chronic cardiac or pulmonary conditions 4
• Uncontrolled diabetes mellitus 4

Chromosomal/Genetic Disorders

• Less likely with normal birth history and healthy siblings, but consider skeletal dysplasias in specific presentations 5

Initial Work-Up Algorithm

Step 1: Detailed Clinical Assessment

• Obtain accurate 3-day food diary documenting all caloric intake, feeding behaviors, and mealtime dynamics 2, 6
• Growth pattern analysis: Plot measurements on WHO charts (under 2 years) or CDC charts (over 2 years); calculate anthropometric z-scores for single-point assessment 7
• Distinguish acute vs. chronic malnutrition: Weight below 3rd percentile with preserved height/head circumference indicates acute malnutrition affecting weight first (organic etiology more likely) 1
• Identify red flags: Vomiting, feeding irritability, respiratory symptoms during feeds, chronic diarrhea, or steatorrhea 1

Step 2: Selective Laboratory Testing (NOT Routine)

Laboratory testing should be reserved for severe malnutrition, concerning symptoms, or failed initial nutritional intervention—routine screening has low yield. 2, 3

First-Tier Testing (When Indicated)

• Complete blood count (CBC) to exclude anemia or systemic disease 1
• Thyroid function tests (TSH, free T4) to exclude hypothyroidism 1
• Celiac screening (tissue transglutaminase antibodies with total IgA) 1
• Comprehensive metabolic panel to assess electrolytes and organ function 1

Second-Tier Testing (Based on Clinical Suspicion)

• Sweat chloride test for cystic fibrosis (sensitivity 90%, specificity 99%) if persistent growth failure with GI symptoms 1
• Fecal elastase to assess pancreatic function if steatorrhea or malabsorption suspected 1
• Video swallow study if aspiration or swallowing dysfunction suspected 1
• Extended 24-hour esophageal pH monitoring, barium swallow, or gastric scintiscan for GERD evaluation when adequate intake with poor weight gain 1

Step 3: Timing for Diagnosis and Intervention

Critical timeframes differ by age:

• Infants (<12 months)**: Persistent inadequate weight gain for **>3 months warrants diagnosis and intervention (infancy is most sensitive to growth-suppressing effects) 1
• Children/adolescents (>12 months): Persistent growth failure for >6 months with height velocity below 25th percentile and height below 3rd percentile 1

Step 4: Referral Indications

Refer to pediatric gastroenterology if:

• Positive or borderline sweat chloride test 1
• Persistent vomiting despite GERD treatment 1
• Suspected swallowing dysfunction or aspiration 1

Hospitalization indicated for:

• Failure of outpatient nutritional management 2
• Suspicion of abuse or neglect 2
• Severe psychosocial impairment of caregiver 2

Common Pitfalls to Avoid

• Do not order extensive laboratory panels routinely—this has low positive predictive value and delays appropriate nutritional intervention 2, 3
• Do not rely on single growth measurements—serial measurements every 2-4 weeks are essential to track response to interventions 1
• Do not miss the combination of adequate oral intake with poor weight gain—this suggests calories are being lost (GERD, malabsorption) rather than simple underfeeding 1
• Do not delay intervention in infants—the first year is critical for preventing irreversible loss of growth potential 1

Monitoring Strategy

• Serial weight measurements every 2-4 weeks initially to assess response to nutritional interventions 1
• Plot all measurements on appropriate growth charts (WHO for <2 years, CDC for ≥2 years) 1, 7
• Reassess at 3 months if outpatient nutritional management initiated; escalate care if no improvement 1