FTT is a common pediatric problem, especially during infancy. The diagnosis of FTT is made when a child’s weight is less than the fifth percentile for weight-for-age or crosses two major percentile lines. Identifying the underlying cause of FTT is usually straightforward, but occasionally it requires an inpatient evaluation. The most important tools for determining the underlying cause of poor growth are a thorough history, complete physical exam, and a staged laboratory workup. There are few other areas in pediatrics where the history is so vitally important. Less often, the exam will hold a clue to the etiology. When the history and physical do not reveal the diagnosis, the laboratory evaluation is not likely to prove helpful. In some cases, carefully selected testing is still in order.

Traditionally, FTT has been classified as organic or nonorganic, although there is often considerable overlap. Many children will have mixed etiologies for their poor growth. Organic FTT reflects an underlying pathophysiologic abnormality, resulting in an inability to ingest, absorb, or utilize adequate nutrition to sustain normal growth. Conditions associated with increased metabolic demands may make the standard caloric intake inadequate. Examples of organic FTT include swallowing disorders, malabsorption, metabolic disorders, and congestive heart failure.

The great majority of FTT is nonorganic and occurs when an otherwise healthy child does not get enough nutrition to sustain normal growth. Difficulties with breastfeeding, caregiver misunderstanding about infant nutritional needs, and improper mixing of formula are three common examples of nonorganic FTT. Often, there are psychosocial factors, such as financial stress or caregiver mental illness, influencing the situation. Most patients with nonorganic FTT are treated successfully as outpatients.