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Quick take: A growth hormone blood test measures growth hormone (GH), a pituitary hormone involved in childhood growth, tissue repair, metabolism, and body composition. The important catch is that GH is released in bursts, not at a steady rate. For that reason, a single random GH result is usually not diagnostic by itself. When clinicians evaluate suspected growth hormone deficiency, acromegaly, gigantism, or pituitary disease, they often combine GH testing with insulin-like growth factor 1 (IGF-1), other pituitary labs, imaging, and sometimes a supervised stimulation or suppression test. MedlinePlus describes GH testing as a group of tests that may include random GH, GH stimulation, and GH suppression testing, depending on whether deficiency or excess is suspected.
What does a growth hormone blood test measure?
Growth hormone is made by the pituitary gland, a small gland at the base of the brain that helps coordinate several hormone systems. GH is especially important for normal growth in children. In adults, it continues to affect muscle, fat, bone, glucose metabolism, and quality-of-life-related functions, although adults no longer need GH for height gain.
The test usually reports GH concentration in serum or plasma, commonly in ng/mL or µg/L depending on the lab. GH acts partly by stimulating production of IGF-1, a hormone made mainly in the liver and other tissues. IGF-1 is often measured with GH because it is more stable over the day and reflects overall growth-hormone activity better than a single GH draw. ARUP Consult notes that a random GH value is limited because GH is secreted in a pulsatile pattern, while IGF-1 is commonly used as a preferred initial test in many evaluations for growth hormone deficiency.
That physiology is the main reason GH testing is different from many routine blood tests. With cholesterol or sodium, one blood draw often gives a useful snapshot. With GH, the value can be low simply because the sample was collected between natural pulses. It can also rise after sleep, intense exercise, stress, fasting, low blood sugar, or certain medications. The result only becomes meaningful when the test type, timing, preparation, symptoms, and related tests are considered together.
Why a clinician may order GH testing
Growth hormone testing is most often ordered when there is a reason to suspect either too little or too much GH, or when a clinician is evaluating broader pituitary function.
- In children, possible GH deficiency may be considered when growth is slower than expected, height is significantly below family pattern, puberty is delayed, or other pituitary problems are suspected. Growth charts, growth velocity, bone age, nutrition, chronic illness, thyroid status, and genetic factors all matter before a GH diagnosis is made.
- In adults, possible GH deficiency is usually evaluated in people with a higher-risk history, such as known hypothalamic or pituitary disease, pituitary surgery or radiation, traumatic brain injury, subarachnoid hemorrhage, stroke, central nervous system infection, or multiple pituitary hormone deficiencies. The Endocrine Society states that confirmation with stimulation testing is usually required in adults unless there is a clear genetic or structural lesion that persists from childhood.
- Possible GH excess may be evaluated when physical findings suggest acromegaly in adults or gigantism in children. In adults, clues can include enlargement of hands or feet, coarser facial features, jaw changes, widening tooth spacing, headaches, sweating, joint pain, carpal tunnel symptoms, sleep apnea, high blood pressure, or diabetes. The Endocrine Society patient resource on acromegaly explains that too much GH raises IGF-1 and is usually caused by a pituitary tumor.
- Monitoring known pituitary or GH-related conditions may involve GH and IGF-1 testing after treatment for acromegaly, during specialist-directed GH therapy, or as part of follow-up after pituitary surgery, radiation, or medication treatment.
GH testing is not typically used as a general wellness screen. It is also not a reliable way to evaluate athletic performance, aging, body composition goals, or non-prescribed hormone use. Because GH levels are difficult to interpret without context, unnecessary testing can create confusing or misleading results.
Types of growth hormone blood tests
The phrase “growth hormone blood test” can refer to several different testing approaches. Understanding which type was ordered is essential before reading the result.
| Test type | What happens | Common use | Main limitation |
|---|---|---|---|
| Random or fasting GH | One blood sample is collected, sometimes after fasting and rest. | May be used as part of a broader pituitary or GH-excess evaluation, or for monitoring in selected cases. | A single value is often not diagnostic because GH is released in pulses. |
| IGF-1 blood test | One blood sample measures IGF-1, usually interpreted with age- and sex-adjusted ranges or z-scores. | Often an initial test for suspected GH excess and a supportive test for suspected GH deficiency. | Can be affected by age, nutrition, liver disease, kidney disease, poorly controlled diabetes, oral estrogen therapy, pregnancy, and assay differences. |
| GH stimulation test | Several GH samples are collected after a medication or stimulus intended to provoke GH release. | Evaluation of suspected GH deficiency. | Requires supervision, takes hours, has protocol-specific cutoffs, and can be affected by body mass index and other factors. |
| GH suppression test | GH is measured before and after drinking a glucose solution. | Evaluation of suspected acromegaly or gigantism when IGF-1 is elevated or equivocal. | Requires fasting, timed samples, glucose handling, and interpretation with IGF-1 and clinical findings. |
Random or fasting growth hormone
A random or fasting GH test is the simplest version: one blood draw. It may be collected in the morning, after fasting, and after a period of rest. Some lab instructions recommend avoiding recent exercise and resting before collection because activity can alter GH. For example, Labcorp’s test information for growth hormone notes that random GH sampling should be performed on fasting patients who have rested before collection.
This type of test can be useful in limited contexts, but it should not be overinterpreted. A low random GH value does not automatically mean deficiency. A higher value does not automatically mean acromegaly. Random GH is best viewed as one data point.
Growth hormone stimulation testing
A GH stimulation test asks a more functional question: can the pituitary gland release GH when stimulated? During the test, a baseline blood sample is collected, a medication or stimulus is given, and additional blood samples are collected over a timed series. Protocols may use agents such as insulin, arginine, glucagon, clonidine, macimorelin, or other specialist-directed methods. The choice depends on age, safety, availability, local practice, and the reason for testing.
The insulin tolerance test has historically been considered a highly validated test in adults, but it intentionally lowers blood sugar and requires close medical supervision. It may not be appropriate for people with seizure disorders, significant cardiovascular disease, or other risk factors. The Endocrine Society adult GH deficiency guideline discusses the need for provocative testing in most adults and notes that testing should be interpreted in the setting of clinical suspicion and other pituitary findings.
Stimulation testing is not the same as ordering a single GH level from an online lab menu. It is usually performed in an endocrinology clinic, hospital outpatient unit, infusion center, or pediatric testing area because timed sampling and monitoring are needed.
Growth hormone suppression testing
A GH suppression test is used when too much GH is suspected. In most people, drinking glucose suppresses GH. In acromegaly, GH may fail to suppress appropriately. MedlinePlus explains that the suppression test typically starts with a fasting morning blood sample, followed by a glucose drink and additional blood samples over the next one to two hours.
For suspected acromegaly, IGF-1 is usually central to the evaluation because it is more stable than GH. The Endocrine Society acromegaly guideline recommends confirming elevated or equivocal IGF-1 with failure of GH suppression after an oral glucose load. Exact thresholds can vary by assay and guideline context, so the lab report and endocrinologist’s interpretation matter.
How to prepare for a growth hormone blood test
Preparation depends on the test type. Always follow the instructions from the ordering clinician or testing site, because GH testing protocols are not interchangeable.
- Fasting: Many GH tests require fasting. Suppression testing and many stimulation protocols require no food for a set number of hours beforehand. MedlinePlus states that eating can change growth hormone stimulation test results and that fasting instructions may be given before testing.
- Exercise: Avoid strenuous exercise before the test if instructed. Exercise can increase GH and may make results harder to interpret.
- Rest before collection: Some random GH samples are drawn after the patient has rested quietly. This helps reduce short-term physiologic variation.
- Medication review: Tell your clinician about prescription medications, over-the-counter drugs, supplements, estrogen therapy, glucocorticoids, diabetes medicines, and any GH or anabolic agents. Do not stop prescribed medication unless the ordering clinician specifically tells you to.
- Illness and glucose control: Acute illness, poorly controlled diabetes, liver disease, kidney disease, nutritional status, and pregnancy can affect interpretation of GH or IGF-1. Your clinician may delay testing or interpret results differently.
- Dynamic test logistics: For stimulation or suppression testing, plan for a longer appointment, timed blood draws, possible IV placement, and monitoring. Ask whether you can drive afterward, especially if the protocol may cause low blood sugar, nausea, drowsiness, or lightheadedness.
For children, preparation may include fasting instructions, activity limits, and a plan for comfort during multiple blood draws. Parents or caregivers should ask how long the visit will take, whether a topical numbing option is available, and what symptoms should be reported during the test.
How to interpret growth hormone results
There is no single “good” GH number that applies to everyone in every situation. Interpretation depends on the reason for testing, the assay, the reference interval, the patient’s age and sex, body size, pubertal stage in children, medications, and whether the sample was random, fasting, stimulated, or suppressed.
If GH is low
A low random GH value is common and often normal because GH secretion is pulsatile. It does not diagnose growth hormone deficiency by itself. If GH deficiency is suspected, clinicians usually look at growth pattern in children, symptoms and pituitary history in adults, IGF-1, other pituitary hormones, and results of a GH stimulation test.
In children, diagnosis is especially clinical and longitudinal. A child’s height percentile alone is not enough; growth velocity, bone age, family heights, pubertal status, nutrition, chronic disease, thyroid function, celiac screening when appropriate, and genetic considerations may all be part of the evaluation. A pediatric endocrinologist may order GH stimulation testing when the overall pattern supports it.
In adults, isolated symptoms such as fatigue, increased body fat, or low muscle mass are not specific for GH deficiency. The likelihood is higher when there is known pituitary or hypothalamic disease, prior pituitary treatment, multiple pituitary hormone deficiencies, or certain neurologic injuries. ARUP Consult notes that adult-onset GH deficiency is most commonly related to hypothalamic-pituitary tumors and their treatment, with other causes including traumatic brain injury and certain central nervous system events.
If GH is high
A high random GH value can occur for reasons that are not acromegaly, including exercise, stress, fasting, sleep-related pulses, and low blood sugar. When GH excess is suspected, IGF-1 is usually a key screening test. If IGF-1 is elevated for age and sex, an oral glucose GH suppression test may be used to see whether GH suppresses appropriately.
Persistently excessive GH before the growth plates close can cause gigantism. In adults, after linear growth is complete, GH excess can cause acromegaly, where bones and soft tissues enlarge over time. Because changes can develop gradually, older photos, ring size, shoe size, dental changes, snoring, sleep apnea, headaches, sweating, joint pain, and metabolic problems can become clinically relevant history.
If IGF-1 is normal
A normal IGF-1 can be reassuring in some settings, particularly when acromegaly is suspected and the clinical picture is not strong. However, it does not always rule out adult GH deficiency. The Endocrine Society guideline notes that normal IGF-1 levels do not exclude GH deficiency in adults, especially when there is other pituitary disease.
If IGF-1 is abnormal
Low IGF-1 may support possible GH deficiency, but it is not specific. It can also be seen with undernutrition, chronic illness, liver disease, poorly controlled diabetes, hypothyroidism, and oral estrogen therapy. High IGF-1 may support GH excess, but laboratories use age-adjusted ranges because IGF-1 changes substantially across childhood, puberty, and adulthood. Borderline or mildly abnormal values often require repeat testing, review of assay-specific reference ranges, and correlation with symptoms.
Limitations and reasons results can be misleading
Growth hormone testing has several built-in limitations. The first is biologic variation: GH rises and falls in pulses. The second is assay variation: different labs and methods may produce different numeric results. The third is clinical context: GH physiology changes with age, puberty, body composition, sleep, exercise, glucose, illness, and medications.
Body mass index is an important example. People with obesity may have a blunted GH response during stimulation testing even without true growth hormone deficiency. ARUP Consult highlights that obesity can reduce stimulation-test responses and that IGF-1 may help support interpretation in that setting. This is one reason endocrinologists avoid diagnosing GH deficiency from a lab cutoff alone.
Dynamic tests also have practical limitations. They take time, may require medications, and can cause side effects such as nausea, flushing, dizziness, sleepiness, or low blood sugar depending on the protocol. Some tests are unsuitable for people with certain medical conditions. For children, stress and repeated sampling can be challenging, and results need to be interpreted with growth data rather than in isolation.
How much does a growth hormone blood test cost?
Cost depends heavily on whether the test is a single GH or IGF-1 blood draw, a multi-sample stimulation or suppression test, where it is performed, and whether insurance is used. A single GH blood draw through an outpatient laboratory is usually far less complex than a supervised stimulation test in a hospital or infusion center.
For insured patients, the out-of-pocket amount depends on plan coverage, deductible status, network rules, prior authorization, and whether the test is considered medically necessary. Medicare and other insurers often reimburse laboratory tests according to fee schedules or contracted rates, but a fee schedule amount is not the same as a patient’s final bill. The CMS Clinical Laboratory Fee Schedule explains that Medicare payment rates for many clinical diagnostic laboratory tests are based on private payor data; including a code on a fee schedule does not automatically mean the test is covered for every circumstance.
For cash-pay testing, compare the effective total cost rather than the advertised test price. A meaningful comparison should include the lab test price, draw fee, physician-order or requisition fee if required, processing or service fees, taxes where applicable, and whether the price includes only one sample or multiple timed samples. GH stimulation and suppression testing may involve facility, nursing, medication, and repeated collection charges, so the total can be much higher than the price of the GH assay alone.
Availability also matters. Some direct-access options may sell a single GH or IGF-1 blood test, but they may not provide a medically supervised dynamic test. State laws and provider policies can also restrict direct-to-consumer lab ordering in certain locations. If your clinician suspects a pituitary disorder, it is often more efficient to ask which exact test protocol, lab, and timing they want before purchasing a test yourself.
What to ask before testing
- Is this a random GH, IGF-1, stimulation test, or suppression test?
- What diagnosis or question is the test meant to address?
- Do I need to fast, avoid exercise, or pause any medication?
- How many blood samples will be collected, and how long will the appointment take?
- Which symptoms during the test should I report immediately?
- Will insurance require prior authorization?
- If paying cash, what is the total price including draw, facility, medication, and administrative fees?
- How will results be interpreted if they are borderline?
Practical next steps after you receive results
If your result is normal, ask whether it answers the clinical question or whether a related test is still needed. For example, a normal random GH may not rule out deficiency, and a normal IGF-1 may not fully exclude adult GH deficiency when pituitary disease is present. If your result is abnormal, avoid assuming the diagnosis from the number alone. Ask whether the result should be repeated, paired with IGF-1, followed by dynamic testing, or evaluated with other pituitary hormones.
If results suggest possible acromegaly or another pituitary disorder, clinicians may order pituitary MRI, visual field testing, glucose and cardiovascular risk evaluation, sleep apnea evaluation, or additional hormone testing. If GH deficiency is being considered, evaluation may include adrenal, thyroid, gonadal, prolactin, and other pituitary-axis tests. Treatment decisions, including whether GH therapy is appropriate, require specialist interpretation because benefits, risks, contraindications, dosing, and monitoring differ by age and diagnosis.
FAQs
Is a growth hormone blood test the same as an IGF-1 test?
No. GH measures growth hormone directly at the time of blood collection. IGF-1 measures a hormone that reflects overall GH activity more steadily. Clinicians often use them together, but they answer different questions.
Can I order a growth hormone blood test myself?
In some states and through some services, consumers can order a single GH or IGF-1 blood test without visiting their own doctor first. That does not mean the result will be sufficient to diagnose a pituitary disorder. Stimulation and suppression testing usually require clinician oversight and a supervised setting.
Why did my clinician order IGF-1 instead of GH?
IGF-1 changes less dramatically throughout the day than GH, so it is often a more useful first-line marker of GH activity. GH may still be needed in a dynamic stimulation or suppression protocol.
What time of day should GH be tested?
Many GH protocols use a morning fasting sample, especially for suppression testing. However, the right timing depends on the test type. Random GH, stimulation testing, and suppression testing each have different instructions.
Does fasting affect growth hormone?
Yes. Food intake and fasting can affect GH physiology, and eating before certain GH tests can change results. Follow the fasting window given by your clinician or lab.
Can exercise affect the result?
Yes. Strenuous exercise can raise GH. If the lab or clinician tells you to avoid exercise before testing, follow that instruction carefully.
What does a borderline result mean?
Borderline results are common in endocrine testing. They may require repeat testing, IGF-1 correlation, review of medications and health conditions, or a supervised dynamic test. The lab number should not be interpreted without the clinical context.
Can children and adults use the same reference range?
No. GH and IGF-1 interpretation differs by age, sex, and pubertal stage. Children are usually evaluated with growth charts, growth velocity, bone age, and pediatric endocrinology context in addition to blood tests.
Does a high GH level mean I have acromegaly?
Not by itself. A high random GH value can happen for several physiologic reasons. Suspected acromegaly is usually evaluated with IGF-1 and confirmation using GH suppression after an oral glucose load when appropriate.
Does a low GH level mean I need growth hormone treatment?
No. A low random GH value is often normal between pulses. GH treatment decisions require a confirmed diagnosis, specialist evaluation, and careful monitoring.
Sources
- MedlinePlus: Growth Hormone Tests
- MedlinePlus Medical Encyclopedia: Growth Hormone Stimulation Test
- MedlinePlus Medical Encyclopedia: Growth Hormone Suppression Test
- ARUP Consult: Growth Hormone Deficiency
- Endocrine Society: Evaluation and Treatment of Adult Growth Hormone Deficiency
- Endocrine Society Clinical Practice Guideline: Acromegaly
- Centers for Medicare & Medicaid Services: Clinical Laboratory Fee Schedule
