Growth Hormone Stimulation Testing
Introduction to Growth Hormone Stimulation Testing
Growth Hormone Stimulation Testing is the gold standard for diagnosing Growth Hormone Deficiency (GHD) in children with growth failure. This dynamic test assesses the pituitary gland's ability to secrete growth hormone in response to pharmacological stimulation.
Key Points:
- Essential diagnostic tool for evaluating short stature
- Requires proper preparation and monitoring
- Multiple sampling over 2-3 hours
- Two separate stimulation tests often required
- Must be performed in specialized centers
Indications:
- Height > 2.5 SD below mean for age
- Growth velocity below 25th percentile
- Significant decrease in growth velocity
- Signs of pituitary dysfunction
- History of cranial radiation
- Structural brain abnormalities
Testing Protocols
Pre-test Requirements:
- Fasting for 8-10 hours
- Normal thyroid function
- Adequate nutrition status
- No acute illness
- Sex steroid priming in prepubertal children (case-dependent)
Sex Steroid Priming Protocol:
- Boys: Testosterone enanthate 100mg IM, 7 days before test
- Girls: Estradiol 1-2mg daily for 2-3 days before test
- Indicated for boys >11 years and girls >10 years with delayed puberty
Safety Considerations:
- Continuous monitoring required
- Emergency equipment availability
- Experienced personnel presence
- Blood glucose monitoring
- IV access maintenance
Growth Hormone Stimulation Agents
Commonly Used Stimulants:
- Clonidine
- Dose: 0.15 mg/m² orally
- Peak response: 60 minutes
- Duration: 120 minutes
- Side effects: Drowsiness, hypotension
- Glucagon
- Dose: 0.03 mg/kg (max 1mg)
- Peak response: 90-120 minutes
- Duration: 180 minutes
- Side effects: Nausea, vomiting
- Arginine
- Dose: 0.5g/kg (max 30g)
- Peak response: 30-60 minutes
- Duration: 120 minutes
- Side effects: Irritation at infusion site
- Insulin
- Dose: 0.05-0.1 U/kg IV
- Peak response: 30-40 minutes
- Duration: 120 minutes
- Side effects: Hypoglycemia
Test Procedure
Sample Collection Schedule:
- Baseline (0 minutes)
- 15 minutes
- 30 minutes
- 45 minutes
- 60 minutes
- 90 minutes
- 120 minutes
Required Equipment:
- Growth hormone collection tubes
- Cold centrifuge
- Timer
- Blood glucose monitoring equipment
- Emergency kit
- IV supplies
Monitoring Parameters:
- Vital signs every 15 minutes
- Blood glucose levels
- Level of consciousness
- Side effects
- IV site integrity
Result Interpretation
Normal Response:
- Peak GH > 10 ng/mL (traditional cutoff)
- Peak GH > 7 ng/mL (using modern ultrasensitive assays)
- Response within 120 minutes
- Return to baseline by 180 minutes
Diagnostic Criteria for GHD:
- Peak GH < 10 ng/mL on two separate stimulation tests
- Peak GH < 7 ng/mL (using modern assays)
- Consider age, puberty status, and BMI in interpretation
Special Considerations:
- Obesity can cause false positive results
- Stress can affect results
- Different assays may have different cutoffs
- Results must be interpreted with clinical context
- Consider IGF-1 and IGFBP-3 levels
Follow-up Actions:
- Positive test: Refer to pediatric endocrinologist
- Borderline results: Consider repeat testing
- Normal results: Consider other causes of growth failure
- Document growth velocity and bone age
