Growth Hormone Tests: Purpose, Test Details & Results

Purpose of Growth Hormone Tests

Growth hormone (GH) plays a vital role in growth, metabolism, and cellular repair throughout life. When the body does not produce enough GH, or produces it in excess, serious health issues can arise. Growth hormone tests were developed to understand and diagnose conditions related to abnormal GH secretion, such as growth hormone deficiency (GHD) or, less commonly, GH excess. These tests help clinicians pinpoint the root of unexplained growth disorders in children, metabolic disturbances in adults, and even some fertility problems. Ultimately, their goal is to guide treatment decisions that can significantly improve patient quality of life.

Why Are Growth Hormone Tests Needed?

GH is essential for normal physical growth in children and for maintaining metabolic health in adults. Deficiency can lead to:

• Short stature in children
• Delayed puberty
• Increased body fat
• Decreased muscle mass and exercise capacity in adults
• Poor quality of life and metabolic issues 1, 4, 5

Conversely, too much GH can cause conditions like acromegaly. Because GH levels naturally fluctuate throughout the day, random blood tests are unreliable. Instead, clinicians use specialized tests to provoke or suppress GH secretion and then measure the response.

Who Benefits from Testing?

Children with unexplained poor growth, short stature, or delayed development are prime candidates for GH testing. Adults may be tested if they show symptoms of GHD—such as fatigue, decreased bone density, or changes in body composition—especially if they have a history of pituitary disease, brain injury, or cranial irradiation 5, 13. Rarely, men with infertility related to spermatogenic arrest may also undergo GH testing 2.

Clinical Decision-Making

Growth hormone tests not only confirm or rule out GH deficiency, but also help clinicians:

• Decide on starting or continuing GH therapy 10, 11, 12
• Monitor response to treatment
• Investigate metabolic or reproductive disturbances 2, 3

Growth Hormone Tests Details

The science of growth hormone testing is complex, as no single test is perfect. Instead, clinicians use a variety of provocative (stimulation) and, less often, suppression tests to evaluate GH status. Each test has its own strengths, limitations, and safety considerations.

Overview of Growth Hormone Testing

Because GH is secreted in pulses and is rapidly cleared from the bloodstream, single random measurements are rarely useful. Instead, tests are designed to "provoke" the pituitary to release GH, so its maximum possible output can be measured and compared to established cut-offs 5, 7.

Insulin Tolerance Test (ITT)

• How it works: Insulin is injected to induce hypoglycemia, which should trigger robust GH release if the pituitary is healthy.
• Pros: Considered the gold standard for both children and adults.
• Cons: Not safe for everyone; contraindicated in those with heart disease, epilepsy, or elderly patients due to the risk of severe hypoglycemia 1, 4, 6, 8.

Glucagon Stimulation Test (GST)

• How it works: Glucagon is administered (usually IM or subcutaneously); this indirectly stimulates GH release.
• Pros: Safer than ITT, suitable when ITT is risky or unavailable.
• Cons: May be less sensitive in certain populations; optimal dosing/cutoffs still being refined 3, 4, 6.

Arginine Stimulation Test (AST)

• How it works: Arginine is infused intravenously, suppressing somatostatin and stimulating GH.
• Pros: Good alternative, especially in children.
• Cons: Not as sensitive or specific as ITT 7, 8, 11.

Levodopa (L-DOPA) and Other Alternatives

• Levodopa can stimulate GH release by increasing dopamine, which inhibits somatostatin.
• Advantages: Oral, well-tolerated.
• Drawbacks: Less commonly used, limited sensitivity 6, 7.

GH-Releasing Hormone (GHRH) Tests

• How it works: GHRH is infused to directly stimulate the pituitary.
• Pros: Very specific, can help differentiate hypothalamic from pituitary causes.
• Cons: Limited availability in some countries, especially the USA 2, 4.

Safety and Limitations

All provocative GH tests carry certain risks—especially ITT, which can cause severe hypoglycemia and, rarely, serious complications in children 1, 4. The choice of test depends on:

• Age and underlying health of the patient
• Availability of the test and expertise
• Specific clinical questions (e.g., hypothalamic vs. pituitary dysfunction)

No single test is perfect. Sensitivity and specificity can be influenced by factors such as obesity, puberty, sex steroid status, and even the time of day 5, 7. Consequently, most guidelines require failure to respond to two different stimuli before diagnosing GHD in children 7.

Growth Hormone Tests Results & Follow-Up

Once growth hormone testing is complete, clinicians must interpret results in context—taking into account the type of test, patient characteristics, and even the laboratory’s assay method. Test results not only confirm the diagnosis but also guide treatment and long-term follow-up.

Interpreting Growth Hormone Test Results

What Defines a ‘Normal’ or ‘Deficient’ Result?

• Cut-off values for GH peak levels vary by test and by laboratory.
• For most adult and pediatric tests, a peak GH < 3–10 ng/mL (or µg/L) after stimulation is considered suggestive of GHD, but exact thresholds differ 8, 10.
• Obesity, puberty, chronic illness, and sex steroids can affect results. For example, obese children may have falsely low responses 5, 7.

False Positives and Negatives

• GH stimulation tests are not perfectly sensitive or specific 5, 10.
  • Sensitivity can be as low as 64–82%, and specificity may be as low as 25% in some studies 10.
• False negatives: Some children/adults with GHD may show a "normal" test response due to technical factors or timing.
• False positives: Some healthy individuals may show a "blunted" response—especially if tests are performed during the day, or if the patient is obese or ill 5, 7.

Special Cases

• Intermediate values: May require repeat testing, different stimuli, or follow-up over time 7, 10.
• Partial GH deficiency: The clinical significance is debated, and treatment decisions may rely on response to GH therapy 7, 12.

Follow-Up After Testing

For those diagnosed with GH deficiency:

• GH therapy is offered to eligible children and adults, with regular monitoring of growth rate, metabolic parameters, and side effects 11, 12.
• Treatment outcomes: Most children with isolated GHD or multiple pituitary hormone deficiencies show significant improvement in growth and final adult height with GH therapy 12.
• Quality of life: Adults treated for GHD report improved well-being, metabolic health, and, in some cases, fertility 2, 11, 13.
• Monitoring: Regular assessment is needed to adjust dosing, monitor for side effects, and track treatment efficacy 11, 12.

For those with normal or equivocal results:

• Further evaluation: If suspicion remains high, repeat or alternative testing may be warranted 7, 10.
• No therapy needed: If GH secretion is adequate and no other pituitary hormone deficiencies are found, treatment is not necessary 1, 7.

Special Populations and Considerations

• Children with Turner syndrome or small-for-gestational-age: May respond less robustly to GH therapy and require individualized management 12.
• Patients with traumatic brain injury: GH deficiency may develop after injury, and testing can guide therapy to improve symptoms and quality of life 13.

Conclusion

Growth hormone tests are a cornerstone in diagnosing and managing disorders of growth and metabolism. They combine clinical judgment, sophisticated testing, and careful follow-up to ensure patients reach their full health potential.

Key takeaways from this article:

• Growth hormone tests are crucial for diagnosing GH deficiency in both children and adults with unexplained growth or metabolic issues.
• Multiple types of stimulation tests are available, each with unique advantages and limitations; ITT is the gold standard but not always safe or practical.
• Interpretation of results requires understanding of the test method, patient factors, and the clinical context.
• GH therapy can dramatically improve growth and quality of life for those with true GH deficiency, but careful follow-up and monitoring are essential for success.
• The field continues to evolve, with new testing modalities and better ways to interpret results on the horizon.

By understanding the purpose, details, and implications of growth hormone testing, patients and clinicians can work together to make informed decisions that support healthy growth and well-being throughout life.