Laboratory Tests for Assessing Growth Hormone Activity in Children
The primary laboratory tests for assessing growth hormone activity in children include growth hormone stimulation tests, insulin-like growth factor-1 (IGF-1) levels, and insulin-like growth factor binding protein-3 (IGFBP-3) measurements, which should be interpreted alongside comprehensive growth chart monitoring.
Growth Assessment Fundamentals
- Growth charts are essential tools for monitoring a child's physical development, with WHO growth charts recommended for children under 24 months and CDC growth charts for children 24 months and older 1, 2
- When using WHO growth charts, values of 2 standard deviations above and below the median (2.3rd and 97.7th percentiles) are recommended for identifying children whose growth might indicate adverse health conditions 1, 2
- Growth velocity, rather than a single measurement, provides more valuable information about a child's growth pattern and should be assessed through serial measurements 3
Laboratory Tests for Growth Hormone Assessment
- Random measurements of serum GH levels are not recommended for screening (except in neonates) as endogenous GH secretion is episodic and pulsatile 4
- Growth hormone stimulation tests are the gold standard for diagnosing growth hormone deficiency, requiring administration of stimulating agents to provoke GH secretion 4, 5
- Insulin-like growth factor-1 (IGF-1) levels serve as a reliable marker of growth hormone activity and are less subject to diurnal variation than direct GH measurements 6, 4
- Insulin-like growth factor binding protein-3 (IGFBP-3) measurements provide additional information about GH activity and are often measured alongside IGF-1 4
Interpreting Test Results
- Multiple factors affect test interpretation including patient age, sex, pubertal status, nutritional state, and assay variability 4
- Different peak GH cut-offs exist by age and test type, requiring careful interpretation by specialists 4
- Growth hormone deficiency may present as isolated or associated with additional pituitary hormone deficiencies, necessitating comprehensive pituitary function testing in some cases 4
Clinical Indications for Testing
- Diminished height velocity and short stature are important clinical markers that should prompt consideration of testing for GH deficiency 6, 4
- Growth disturbances, including short stature or growth failure, could indicate chronic disease, nutritional deficits, celiac disease, or hormonal abnormalities 6, 7
- Children whose growth parameters fall below the 2nd percentile should be evaluated for potential underlying causes 3
Growth Hormone Treatment Considerations
- In the United States, there are 8 FDA-approved indications for pediatric GH therapy, including GH deficiency, Turner syndrome, and idiopathic short stature 5
- Treatment decisions should be based on accurate diagnosis through appropriate laboratory testing and growth assessment 5
- Regular monitoring of growth parameters is essential for tracking response to GH therapy 3
Common Pitfalls in Growth Assessment
- Relying on a single growth measurement rather than evaluating growth velocity over time 7, 8
- Failing to consider the transition point at age 2 years when switching from WHO to CDC growth charts 9
- Not accounting for assay variability when interpreting GH and IGF-1 test results 4
- Overlooking the need for comprehensive evaluation of other pituitary hormones in cases of suspected GH deficiency 4