Measurement of GH is primarily of interest in the diagnosis and treatment of various forms of inappropriate growth hormone secretion.
Human growth hormone (HGH), also known as growth hormone (GH), is a hormone secreted by the anterior pituitary gland.
This blood test is often used to evaluate a growth hormone deficiency that is causing slowed growth. It is also used to measure overall pituitary function as well as measure replacement therapy. It can also be prescribed as an anti-aging treatment in some cases.
What is a growth hormone test?
The growth hormone test, or HGH test, measures the growth hormone blood level.
Why is an HGH test important?
This HGH blood test can help identify a growth hormone deficiency or excess.
Is there any special preparation required before getting an HGH blood test?
If possible, please avoid exercise for 30 minutes before getting this growth hormone lab test.
What type of specimen will I submit?
This Growth Hormone Test is a blood test.
Do I need to fast to take this test?
An 8-12 hour fast is recommended before testing.
How long does it take to get test results?
It typically takes 4 business days or less.
Laboratory testing for GHD is appropriate in adult patients with:
- Evidence or history of the hypothalamic-pituitary disease (including hypothalamic-pituitary tumors)
- Symptoms suggestive of GHD or pituitary dysfunction (eg, low lean body mass, increased body fat, dyslipidemia, cardiac dysfunction, low muscle strength, low exercise capacity, low bone mineral density, increased insulin resistance, decreased fibrinolysis, premature atherosclerosis)
- History of traumatic brain injury, subarachnoid hemorrhage, ischemic stroke, or central nervous system infection
Laboratory Testing
Test Methods
Two types of tests, static and stimulation, are used in the diagnosis of GHD.
Static Tests
Static tests entail a one-time measurement of a component of the GH axis. Due to the lack of harmonization between assays, the use of the same assay throughout evaluation and diagnosis is recommended.
Laboratory-specific and age-adjusted reference intervals are also recommended.
Static tests are also useful in monitoring.
Static Tests for GHD
| Test | Uses | Limitations |
|---|---|---|
| IGF-1 | Preferred initial test for GHD Concentrations are less variable than GH concentrations Low concentration in the absence of a catabolic condition (eg, diabetes) is strong evidence for GHD; stimulation testing is recommended | Low concentration is suggestive of GHD, but insufficient to diagnose GHD, and may be secondary to another condition (eg, uncontrolled diabetes, liver disease, or oral estrogen therapy) Normal concentration does not rule out GHD |
| GH | Aids in diagnosis of GH excess or deficiency disorders | Single, random GH result is nondiagnostic because GH is produced in a pulsatile fashion |
| IGFBP-3 | Can be used in addition to GH concentration and IGF-1 testing to investigate suspected anterior hypopituitarism; concentrations reflect IGF-1 concentrations | Low concentration is suggestive of GHD, but insufficient to diagnose GHD |
Stimulation Tests
In most cases, standalone static testing is not sufficient for the diagnosis of GHD and should be followed up with stimulation tests.
Stimulation tests (also referred to as provocative tests) entail the administration of a drug, followed by repeat testing for GH over time to assess the body’s response. Stimulation tests are only recommended if there is reasonable clinical suspicion of GHD and there is the intent to treat with rhGH if the diagnosis is confirmed.
Stimulation Tests for GHDa
| Test | Description | Limitations | Peak GH Cutpoints |
|---|---|---|---|
| GST | Safe and accurate test for GHD if appropriate BMI-adjusted GH cutpoints are used | Diagnostic accuracy in patients with glucose intolerance is unknown Long duration, multiple blood draws, requires intramuscular administration May cause gastrointestinal side effects | Children: <5.0 ng/mLb Transition patients and adults: ≤3.0 ng/mL if normal weight ≤3.0 ng/mL if overweight with high pretest probability of GHD ≤1.0 ng/mL if overweight with low pretest probability of GHD ≤1.0 ng/mL if obese |
| ITT | “Gold standard” test in adults | Safety concerns in certain patient populations Laborious May cause severe hypoglycemia Contraindicated in patients >60 yrs, patients with seizure disorders, and patients with cardio/cerebrovascular disease | Children: <5.0 ng/mLb Transition patients and adults: ≤5.0 ng/mL |
| Macimorelin test | Suitable alternative when ITT is contraindicated; FDA approved for adult GHD in 2017 | Intraindividual variability Appropriate reference values have not been determined for many populations (eg, patients with a BMI >40 kg/m2) Costly | Children: <5.0 ng/mLb Transition patients and adults: ≤2.8 ng/mL |
Adult-Onset Growth Hormone Deficiency
Diagnosis
Static serum GH and IGF-1 levels are insufficient to diagnose AOGHD unless the patient has an organic hypothalamic-pituitary disease with a deficiency in at least three pituitary hormone axes, known genetic defects, or structural hypothalamic-pituitary defects.
Stimulation testing should be performed only after all other pituitary hormone deficiencies have been treated and dosing is stable.
Two positive stimulation tests are suggested to make a diagnosis of idiopathic GHD in adults without suggestive clinical circumstances because there is a high false-positive rate for single stimulation tests.
Patients with obesity will often appear to have a decreased response to stimulation tests despite a lack of true GHD deficiency; therefore, an IGF-1 test may be useful to support the diagnosis in this population.
Treatment Dosing
IGF-1 is the recommended test to guide rhGH dose determination in adults, although IGF-1 levels are only weakly correlated with clinical endpoints.
Although there are insufficient data to determine the ideal target serum IGF-1 concentration, maintaining a target serum IGF-1 level within the age-adjusted, laboratory-specific reference range is recommended (depending on clinical circumstances and the patient’s pretreatment IGF-1 level).
A 1-2 month retest interval for dose adjustment is recommended, as is the use of the same assay that was used in the diagnosis of GHD.
Treatment Monitoring
In adults treated with rhGH, IGF-1 testing is recommended at 6-12 month intervals once a suitable maintenance dose has been achieved.
Shorter intervals may be appropriate depending on the clinical circumstances (eg, in elderly patients or patients with diabetes mellitus).
GH may interact with other pituitary hormones, including the thyroid and glucocorticoid hormone axes.
Monitoring of the thyroid axis should include free T4 because GH replacement is associated with reduced free T4 levels.
Monitoring the adrenal axis and adrenal function is recommended.
Hemoglobin A1c and cortisol or cosyntropin stimulation tests may be appropriate, depending on the clinical circumstances.
Fasting lipids are recommended at 6-12 month intervals due to the increased risk of cardiovascular morbidity and mortality in adult patients with GHD.
For any additional concerns be sure to contact our team of experts and apply for a free consultation.