Criteria for Diagnosing Failure to Thrive in Children
Failure to thrive (FTT), now preferably termed "growth faltering," is diagnosed when a child's weight and/or height falls below the 10th percentile on appropriate growth charts, or when there is inadequate weight gain over time as measured by anthropometric z-scores, with the most reliable criterion being slow conditional weight gain (weight gain adjusted for birthweight) combined with low body mass index. 1, 2, 3
Core Diagnostic Criteria
Anthropometric Measurements
The diagnosis relies solely on anthropometric parameters, with weight being the predominant indicator: 4
Weight and/or height ≤10th percentile when plotted on racially or ethnically appropriate growth curves 5, 6
Anthropometric z-scores are now the recommended method for assessment, as traditional criteria can be imprecise and difficult to track over time 2
- Z-scores can be calculated with a single set of measurements to assess malnutrition severity 2
Slow conditional weight gain (weight gain adjusted for birthweight) is the most reliable single criterion, particularly when combined with low BMI 3
- This identifies children with prenatal growth retardation and early developmental delays 3
Growth Pattern Assessment
Serial measurements are essential for diagnosis: 6
- Weight measurements every 2-4 weeks initially to track response to interventions 6
- Downward crossing of centiles on weight-for-age charts, though this criterion alone may identify healthy low-risk infants in affluent populations and has poor specificity 3
Clinical Examples with Specific Measurements
Example 1: Acute Malnutrition (Organic FTT)
A 6-month-old infant with:
- Weight below 3rd percentile
- Height at 25th percentile
- Head circumference at 25th percentile
- Irritability during feeding with multiple vomiting episodes 6
This pattern indicates acute malnutrition affecting weight first, which is a critical distinguishing feature of organic FTT. 6 The disproportionate growth failure (weight only affected rather than global growth delay) combined with specific GI symptoms suggests an organic etiology requiring immediate gastroenterology evaluation. 6
Example 2: Growth Faltering with Multiple Criteria
An infant meeting one or more of these criteria:
- Low weight for age (below 10th percentile) 5
- Low BMI for age 7
- Slow conditional weight gain 3
- Waterlow's criterion for wasting 7
Approximately 27% of infants may meet one or more criteria, though concurrence among different criteria is generally poor, with most children identified by only one criterion. 7
Distinguishing Organic from Non-Organic Causes
Red Flags for Organic Etiology
Specific clinical features that mandate further investigation: 8
- Chronic respiratory symptoms: tachypnea, hypoxemia, increased work of breathing 8
- Gastrointestinal symptoms: vomiting, diarrhea, signs of malabsorption 8
- Metabolic derangements: hepatomegaly with metabolic abnormalities 8
- Dysmorphic features suggesting genetic syndromes 8
- Feeding-specific symptoms: irritability during feeding, swallowing dysfunction, aspiration risk 6, 8
Pathophysiologic Categories
FTT results from three main mechanisms: 9
- Inadequate caloric intake: difficulties with nursing, limited food availability, incorrect formula preparation 9
- Inadequate caloric absorption: metabolic, gastrointestinal, or other medical conditions (celiac disease, cystic fibrosis, pancreatic insufficiency) 8, 9
- Excessive caloric expenditure/ineffective utilization: hyperthyroidism, diabetes, pulmonary or cardiac conditions 9
Initial Diagnostic Workup
Laboratory Screening
Basic screening tests should be obtained when organic causes are suspected: 6
- Complete blood count (CBC) to exclude anemia 6
- Thyroid function tests (TSH, free T4) 6
- Celiac disease screening (tissue transglutaminase antibodies with total IgA) 6
- Sweat chloride test for cystic fibrosis (sensitivity 90%, specificity 99%) 6
- Fecal elastase to assess pancreatic function in suspected pancreatic insufficiency 6
Specialized Testing
When specific symptoms are present: 6
- Video swallow study to assess swallowing dysfunction and aspiration risk 6
- Extended 24-hour esophageal pH monitoring, barium swallow, and gastric scintiscan to evaluate for GERD 6
Common Pitfalls
Avoid these diagnostic errors:
- Using downward crossing of centiles alone as the sole criterion, as this may identify healthy low-risk infants rather than true FTT, particularly in affluent populations 3
- Failing to adjust for birthweight when assessing weight gain—conditional weight gain is more reliable than absolute weight measurements 3
- Missing the distinction between weight and height faltering: children with low weight-for-height tend to be relatively tall, which may represent a different growth pattern 7
- Delaying diagnosis in the first two years of life, as failure to recognize and treat growth faltering during this critical period may result in decreased adult height and cognitive potential 2
When to Refer
Referral to pediatric gastroenterology is indicated when: 6