Assessing Adequate Growth Hormone Levels in Adolescents
Introduction to GH Assessment
- The Endocrine Society recommends that adequate growth hormone (GH) levels in adolescents be assessed functionally, considering normal GH secretion is demonstrated when GH suppresses below a certain threshold after an oral glucose load, although this cutoff is problematic in adolescents, with approximately 30% of normally growing tall children failing to suppress below this threshold 1.
Clinical Indicators of Adequate GH Function
- The American Academy of Pediatrics suggests that normal growth velocity, defined as height velocity at or above the 25th percentile for age and sex, indicates sufficient GH action 3.
- Appropriate pubertal progression, assessed using Tanner staging, should show age-appropriate sexual development, as pubertal delay can indicate GH-related issues 6.
- The Endocrine Society recommends that serum IGF-1 levels should fall within local Tanner stage-matched, sex-matched, and age-matched normal ranges, though this must account for inter-assay variability 1.
Important Caveats for Adolescent GH Testing
- The American College of Endocrinology notes that standard adult GH suppression testing is unreliable in adolescents, with approximately 30% of children with tall stature failing to suppress GH below 1 μg/L after glucose load despite being completely normal 1.
- The Society for Pediatric Endocrinology states that IGF-1 interpretation requires proper reference ranges, as values can be falsely low with concurrent hypothyroidism, malnutrition, or severe infection, and falsely elevated with poorly controlled diabetes, hepatic/renal failure, or in girls taking oral estrogens 1.
Practical Clinical Approach
- The American Academy of Pediatrics recommends plotting growth parameters, including current height, height velocity over the past 6-12 months, and parental target height, to assess growth concerns in adolescents 3.
- Assessing pubertal development by documenting Tanner stage is essential to contextualize GH dynamics 3, 1, 6.
- Obtaining a bone age radiograph, such as a left wrist X-ray, can help assess growth potential and whether epiphyses remain open 3, 6.
- Measuring IGF-1 and thyroid function, including serum IGF-1 and TSH/free T4, can help exclude hypothyroidism and assess GH function 1, 6, 2.