What's the difference between IGF-1 and growth hormone testing?

Growth hormone levels fluctuate dramatically throughout the day, making single measurements unreliable. IGF-1 levels remain relatively stable, providing a better indicator of average growth hormone activity over time. This makes IGF-1 testing more practical and reliable for assessing growth hormone function.

Can medications or supplements affect IGF-1 results?

Yes, certain factors can influence IGF-1 levels. High-dose biotin supplements should be stopped 72 hours before testing to avoid interference. Growth hormone therapy, testosterone replacement, and some other medications may affect levels. Nutritional status also significantly impacts results.

Why do IGF-1 reference ranges vary so much by age?

IGF-1 levels change dramatically throughout life, peaking during puberty and gradually declining with age. Children and adolescents typically have much higher levels than adults, and levels continue to decrease with aging. This is why age-adjusted reference ranges and Z-scores are essential for proper interpretation.

What happens if my IGF-1 levels are abnormal?

Abnormal results don't provide a diagnosis on their own but indicate the need for further evaluation. Low levels may suggest growth hormone deficiency or other conditions, while high levels could indicate excess growth hormone production. Additional testing and consultation with an endocrinologist may be recommended.

Can adults with normal growth benefit from knowing their IGF-1 levels?

Adults may find IGF-1 testing valuable for evaluating unexplained fatigue, changes in body composition, bone health concerns, or metabolic issues. While growth hormone deficiency is less common in adults, understanding IGF-1 levels can provide insights into overall hormonal health and aging processes.

How accurate are IGF-1 tests for diagnosing growth hormone problems?

IGF-1 testing is highly valuable but not definitive alone. Very low levels strongly suggest growth hormone deficiency, especially in children. However, some individuals with mild growth hormone issues may have normal IGF-1 levels. The test is most useful when interpreted alongside clinical symptoms and other hormone assessments.

Hormones

IGF-1 (Growth Hormone Marker)

Measures insulin-like growth factor 1 to evaluate growth hormone activity and diagnose growth disorders, pituitary conditions, and metabolic imbalances.

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What this test measures

IGF-1 (insulin-like growth factor 1) is a hormone that mediates most of the growth-promoting effects of growth hormone (GH) throughout the body. When the pituitary gland releases GH, the liver responds by producing IGF-1, which then acts on bones, muscles, and other tissues to promote growth and repair. Together, GH and IGF-1 are the primary drivers of normal skeletal and tissue development.

The test measures IGF-1 rather than GH directly because GH is released in short bursts and fluctuates dramatically based on sleep, exercise, meals, and time of day. IGF-1, by contrast, circulates at relatively stable levels that reflect average GH activity over time, making it a far more practical and reliable marker. Healthcare providers use the IGF-1 test to evaluate growth disorders in children, screen for GH deficiency or excess in adults, and monitor treatment in patients receiving growth hormone therapy.

Who should consider this test

You might consider this test if you are experiencing any of the following:

Individuals with unexplained growth concerns in children or adolescents who may be growing too slowly or too rapidly for their age
Adults experiencing unexplained fatigue, decreased muscle mass, or reduced bone density that could indicate growth hormone deficiency
Those with suspected pituitary disorders, including potential tumors that could affect growth hormone production
Individuals being monitored for acromegaly or other growth hormone excess conditions
Patients undergoing growth hormone replacement therapy who need treatment monitoring
People with nutritional disorders or chronic illnesses that may affect growth hormone function

What to expect

Preparation

No special preparations are needed for an IGF-1 test. Individuals should inform their healthcare provider about any medications or supplements they're taking, particularly biotin supplements which should be discontinued 72 hours before testing if taking high doses.

Sample Type

A standard blood draw from a vein in the arm using a small needle

Collection

A healthcare professional will take a blood sample from a vein in the arm using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial.

Turnaround

Results are typically available within 2-4 business days after the sample reaches the laboratory

Understanding your results

IGF-1 reference values are heavily age-dependent: levels are highest during puberty and adolescence and decline steadily through adulthood. For this reason, results must always be compared to age- and sex-matched reference ranges. Many laboratories report a Z-score alongside the raw value, indicating how far the result falls above or below the population mean for the relevant age and sex group. Healthcare providers interpret IGF-1 results in combination with clinical symptoms, growth data (in children), and sometimes additional stimulation tests to arrive at a complete assessment of growth hormone function.

Population	Reference Range	Notes
Adults (varies by age)	Approximately 34-548 ng/mL	Ranges vary by lab, assay method, and are often expressed as a Z-score that adjusts for age and sex
Z-score interpretation	-2.0 to +2.0	Results that are within the IGF-1 reference interval will have a Z score between -2.0 and +2.0

Reference ranges shown are general guidelines. Your lab report will include the specific reference range used by the laboratory that processed your sample, which is the authoritative range for interpreting your results.

What does a “Low” result mean?

Lower than normal levels of IGF-1 probably indicate growth hormone deficiency or insensitivity to GH. In children, this may be caused by a genetic disorder or brain disease. Low IGF-1 levels: especially when below the age-specific reference range: can point to growth hormone deficiency, GH resistance, malnutrition, or chronic illness. Persons with anorexia or malnutrition have low values of IGF-1, and malnutrition results in low serum IGF-1 concentrations, which recover with restoration of adequate nutrition.

What does a “High” result mean?

Higher than normal levels of IGF-1 may indicate gigantism in children or acromegaly in adults. These conditions are most often caused by a tumor in the pituitary gland. Elevated IGF-1 is often associated with conditions like acromegaly, usually due to excess GH secretion, often caused by a pituitary tumor. High levels may also be associated with other conditions affecting growth hormone production or certain medications that influence IGF-1 levels.

Privacy & confidentiality

All test orders are authorized and results reviewed by an independent, board-certified physician who is not the patient's personal doctor. Your IGF-1 test results are completely confidential and handled with the utmost discretion. Results are not reported to your personal doctor unless you specifically request it, and they are not part of your medical records maintained by your healthcare provider. The test results will not appear on insurance statements or explanation of benefits, ensuring complete privacy regarding your hormone testing. Your employer, insurance company, or any third parties will not have access to your results. This confidential testing allows individuals to understand their growth hormone status privately, with no doctor visit required to order the test. All results are delivered securely and can be shared with healthcare providers at your discretion.

Frequently asked questions

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Last reviewed: April 2026

CPT Code: 84305

This test may not be available in: NY, NJ, RI

This page is for informational purposes only and does not constitute medical advice. Always consult with a healthcare provider regarding any health concerns. LevelPanel does not diagnose, treat, or prescribe.

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