Growth Hormone Test For Adults: When And Why To Test

What Does Growth Hormone Do in Adults?

The anterior pituitary gland releases GH in short pulses regulated by hypothalamic signaling, primarily growth hormone-releasing hormone (GHRH) and somatostatin. In adults, GH contributes to lean body mass, bone mineral density, lipid metabolism, and cardiovascular function (Molitch et al., 2011). Most of its downstream effects happen through IGF-1, a hormone produced mainly by the liver in response to GH stimulation. IGF-1 has a longer half-life and stays more stable across the day than GH itself, which is why it serves as the primary screening marker for growth hormone status.

GH output declines with age. That decline is physiologic and, on its own, doesn't meet the criteria for a treatable deficiency. Guidelines draw a clear boundary between the normal age-related drop in GH secretion and pathologic AGHD, which has an identifiable pituitary or hypothalamic cause and meets biochemical thresholds on stimulation testing (Yuen et al., 2019). Ordering an IGF-1 blood test can flag whether further evaluation is warranted, but a low or low-normal result by itself doesn't confirm the condition.

Signs That May Point to Growth Hormone Deficiency

AGHD presents subtly. Unlike childhood GH deficiency, which shows up as measurably slow growth against standardized charts, adult GHD lacks a single visible endpoint. Symptoms overlap with dozens of other conditions, and that overlap is the reason guidelines require biochemical confirmation before any clinical determination is made.

Symptoms that may lead a provider to consider GH testing include increased body fat concentrated around the abdomen, reduced lean mass, decreased exercise tolerance, low bone mineral density, unfavorable lipid shifts such as higher LDL cholesterol paired with lower HDL, persistent fatigue, and changes in mood or concentration. Changes in skin and hair have also been reported in clinical series.

None of these symptoms, individually or together, are enough to establish AGHD. The Endocrine Society states that stimulation testing should not be pursued in adults with nonspecific complaints like fatigue or weight gain unless the person has a documented history of organic hypothalamic-pituitary disease, pituitary surgery, cranial radiation, or head trauma (Molitch et al., 2011). Clinical context is what separates a diagnostic workup from unnecessary screening.

The most common causes of AGHD include pituitary tumors and the fallout from their treatment (surgery, radiation), traumatic brain injury, and congenital pituitary disorders. Less often, infections, inflammatory conditions, or vascular damage to the pituitary are responsible. In some cases, no identifiable cause is found.

How Is Adult Growth Hormone Deficiency Diagnosed?

Diagnosis follows a two-step pathway: screening blood work, then confirmatory stimulation testing.

The first step is an IGF-1 blood draw. A result below -2.0 standard deviation scores (SDS) for age, in an adult with supporting clinical history, raises suspicion and justifies moving to stimulation testing. A normal IGF-1 doesn't rule out AGHD. Many adults with confirmed deficiency carry IGF-1 values inside the age-adjusted reference range, because IGF-1 sensitivity is limited as a standalone measure (Yuen et al., 2019). This makes IGF-1 a useful first pass rather than a final answer. Marek Diagnostics lists IGF-1 among its individual biomarkers, and it can also be included in a broader lab panel.

The second step is a growth hormone stimulation test. A stimulation test administers a substance that triggers the pituitary to release GH, then tracks the response through blood draws collected at timed intervals over 1-4 hours. If the peak GH response stays below a test-specific threshold in the appropriate clinical context, the finding supports a diagnosis of AGHD. This step is required in most clinical scenarios.

Stimulation testing can be bypassed in a few specific circumstances: adults with documented organic hypothalamic-pituitary disease who already carry 3 or more other pituitary hormone deficiencies and an IGF-1 below -2.0 SDS don't need a provocative test. The same exception applies to genetic defects affecting the hypothalamic-pituitary axis and structural brain defects (Molitch et al., 2011; Yuen et al., 2019).

Before any stimulation test, other pituitary hormone deficiencies (thyroid, cortisol, sex hormones) should be identified and replaced where appropriate. Unaddressed deficiencies can skew GH test results and lead to misinterpretation.

Types of Growth Hormone Stimulation Tests

Three stimulation tests are used in the US for diagnosing AGHD. Each carries different trade-offs in accuracy, safety, and practicality.

The ITT remains the reference standard (Yuen, 2023). It requires supervised medical monitoring because of the risk of severe hypoglycemia. For that reason, many centers use the GST when the ITT is contraindicated or impractical.

Body mass index affects results. The standard GST threshold of 3 mcg/L can misclassify AGHD in adults with obesity, because excess body fat blunts the GH response to glucagon regardless of pituitary function. In a prospective study comparing the GST to the ITT, Hamrahian et al. found that lowering the threshold to 1 mcg/L yielded 92% sensitivity and 100% specificity (Yuen, 2023). The 2019 AACE guideline adopted BMI-stratified thresholds for this reason (Yuen et al., 2019).

Macimorelin received FDA approval in December 2017 as the only oral diagnostic test for AGHD. It's shorter, better tolerated, and unaffected by age, sex, or BMI in validation studies. Commercial availability has been intermittent since 2023 following a distribution change, so providers should confirm supply before ordering.

What Do Growth Hormone Test Results Mean?

A peak GH below the test-specific threshold during stimulation, combined with clinical context, supports a diagnosis of AGHD. No single number stands alone. Providers weigh the stimulation result against medical history, other pituitary hormone findings, and any imaging.

A borderline result, near the threshold, calls for careful reading. GH immunoassays use different antibody specificities and calibration standards, so a value from one laboratory isn't directly comparable to a result from another. The measured GH should be read against the same assay and reference range that established the threshold. Repeat testing may be appropriate when the result doesn't match the clinical picture, and the 2019 AACE guideline recommends using two separate stimulation tests when pretest probability is low (Yuen et al., 2019).

Adults being evaluated should prepare for blood work by fasting as directed and disclosing all current medications. Oral estrogen, corticosteroids, and certain other drugs can affect IGF-1 and GH measurements.

If testing supports a diagnosis of AGHD, the next step is a treatment evaluation with a provider. If results are normal, the symptoms have a different cause and the workup should shift direction.

Treatment After Confirmed Growth Hormone Deficiency

When treatment is pursued, the standard FDA-approved option is recombinant human growth hormone (somatropin), given as a subcutaneous injection. The decision to begin replacement is made between the provider and the individual after weighing expected benefits against potential risks. Multiple daily formulations have been on the market for years. In July 2025, the FDA approved once-weekly lonapegsomatropin (Skytrofa) for adults with documented GHD, based on the foresiGHt trial. That trial reported reductions in trunk fat percentage and increases in lean mass relative to placebo, with a safety profile similar to daily somatropin. Individual responses vary.

Providers typically start at a conservative amount and adjust based on clinical response, side effects, and age-adjusted IGF-1 measured through serial lab work. Common side effects of replacement include fluid retention, joint discomfort, and carpal tunnel symptoms. Providers can often manage these by adjusting the prescribed amount.

Long-term monitoring includes periodic IGF-1, glucose or HbA1c, lipids, and assessment for fluid retention or joint symptoms. Adults considering this evaluation pathway can review how lab ordering works through Marek Diagnostics.

Recombinant GH is contraindicated in active cancer, among other conditions; a provider reviews the full list of contraindications before prescribing. In adults with diabetes, careful glucose monitoring is standard because GH can increase insulin resistance.

Non-approved GH secretagogue peptides aren't substitutes for approved recombinant GH in documented AGHD. Their compounding status is subject to ongoing FDA rulemaking, and clinical guidelines don't support their use for this condition.

A growth hormone test for adults begins with an IGF-1 draw and, when the clinical picture warrants it, proceeds to a supervised stimulation protocol. Anyone with persistent symptoms alongside a known pituitary or hypothalamic condition should discuss testing with a provider. A general health panel that includes IGF-1 can serve as a practical first step toward answers.

Disclaimer: This blog post is intended for informational purposes only and should not be considered medical advice. Always consult a healthcare professional before making changes to your health routine.

FAQs

Is a single IGF-1 blood test enough to diagnose adult growth hormone deficiency?

No. A low IGF-1 supports further investigation but doesn't confirm AGHD on its own. Many adults with confirmed deficiency have IGF-1 within the normal age-adjusted range, so a normal result doesn't exclude the condition either. The Endocrine Society and the AACE both require a stimulation test for confirmation in most clinical scenarios (Molitch et al., 2011; Yuen et al., 2019).

What is the most accurate growth hormone test for adults?

The insulin tolerance test (ITT) is considered the reference standard for diagnosing AGHD. Macimorelin, an oral test approved by the FDA in 2017, has comparable accuracy and is shorter, though its commercial availability has varied since 2023. The glucagon stimulation test is widely used as an alternative when the ITT is contraindicated (Yuen, 2023).

Does body weight affect growth hormone test results?

Yes. Adults with higher body mass index produce less GH in response to stimulation, regardless of whether the pituitary is healthy. Using the standard glucagon stimulation test threshold of 3 mcg/L in adults with a BMI above 30 can produce a false-positive test result. The 2019 AACE guideline recommends a lower threshold of 1 mcg/L for this group (Yuen et al., 2019).

How rare is adult growth hormone deficiency?

Confirmed AGHD is very uncommon. A 2025 US analysis estimated prevalence at 0.2 per 100,000 for confirmed cases and 37 per 100,000 for confirmed plus at-risk cases (Hoffman et al., 2025). It most often results from pituitary tumors, pituitary surgery, cranial radiation, or head trauma, not from normal aging.

Does age-related decline in growth hormone mean I need testing?

Not typically. GH secretion drops with age in all adults, and that decline is considered a normal physiologic process. Clinical guidelines distinguish age-related reduction from pathologic AGHD, which has an identifiable pituitary or hypothalamic cause and meets specific biochemical thresholds on provocative testing (Molitch et al., 2011).

Can a growth hormone test for adults be done through a telehealth provider?

IGF-1 screening can be ordered through a telehealth provider like Marek Diagnostics and completed at a local lab. Provocative stimulation testing, which requires monitored injection and serial blood draws over 1-4 hours, is typically performed in a specialized clinical setting such as an endocrinology office.

Are growth hormone secretagogue peptides an alternative to testing or treatment?

Peptides such as CJC-1295, Ipamorelin, and GHRP-2 aren't FDA-approved for any indication, including diagnosis or treatment of AGHD. FDA compounding policy has restricted many of them, and clinical guidelines don't support their use as substitutes for approved recombinant growth hormone in documented deficiency.

References

• J Clin Endocrinol Metab. 2011;96(6):1587-1609

• Endocr Pract. 2019;25(11):1191-1232

• Endotext. South Dartmouth (MA): MDText.com, Inc.; Updated 2023 Aug 8

• Adv Ther. 2025;42:2853-2873