Infants or children who fail to thrive have a height, weight, and head circumference that do not match standard growth charts. The person's weight falls lower than 3rd percentile (as outlined in standard growth charts) or 20% below the ideal weight for their height. Growing may have slowed or stopped after a previously established growth curve.

The following are delayed or slow to develop:

• Physical skills such as rolling over, sitting, standing and walking
• Mental and social skills
• Secondary sexual characteristics (delayed in adolescents)

The doctor will perform a physical exam and check the child's height, weight, and body shape. A detailed history is taken, including prenatal, birth, neonatal, psychosocial, and family information.

A Denver Developmental Screening Test reveals delayed development. A growth chart outlining all types of growth since birth is created.

The following laboratory tests may be done:

• Complete blood count (CBC)
• Electrolyte balance
• Hemoglobin electrophoresis to determine the presence of conditions such as sickle cell disease
• Hormone studies, including thyroid function tests
• X-rays to determine bone age
• Urinalysis