How to Test Your IGF-1 (And What the Number Means)

If you have spent any time reading about growth hormone, recovery, or aging, you have probably run into IGF-1. It shows up in longevity podcasts, hormone clinic panels, and supplement marketing. What almost nobody explains is the practical part: how to test your IGF-1, what to do before the blood draw, and how to read the number without drawing the wrong conclusion from it.

That gap matters, because IGF-1 is one of the easiest lab values in endocrinology to misinterpret. The same blood sample can produce meaningfully different numbers at two different labs. A "normal" result does not rule out a growth hormone problem. A low result usually says more about your diet, thyroid, or liver than your pituitary. And the reference range shifts underneath you every few years as you age.

Here is what the test actually involves, what the number means in context, and where it fits in a broader picture of men's health.

Quick Summary

• IGF-1 (insulin-like growth factor 1, formerly called somatomedin C) is a liver-made hormone produced in response to growth hormone. It is measured instead of GH because GH secretion is pulsatile with significant diurnal variation, while IGF-1 shows only minor fluctuations, making it a stable, integrated measure of GH production and tissue effect. Mayo Clinic Laboratories

• Ordering is simple. It is a single serum blood draw, CPT code 84305, available through most clinicians and through direct-to-consumer lab services. Direct-to-consumer prices run roughly $20 to $140 before a draw fee. Mito Health

• Fasting is generally not required, but biotin is a real problem. Mayo Clinic Laboratories instructs patients to avoid biotin-containing supplements for 12 hours before collection, because biotin can make IGF-1 results falsely low; some labs advise stopping biotin 72 hours ahead. Mayo Clinic LaboratoriesWalk-In Lab

• Age and sex determine your reference range, not a universal "good" number. Male intervals fall from roughly 115 to 355 ng/mL in the early twenties to roughly 67 to 205 ng/mL between 46 and 50, per Mayo Clinic Laboratories' published intervals.

• Ask for the Z-score. A result inside the reference interval corresponds to a Z-score between -2.0 and +2.0, which is far easier to track over time than a raw number. ARUP Laboratories

• High IGF-1 is a screening flag, not a diagnosis. Confirmation of acromegaly historically required failure to suppress GH below 1 µg/L during a 75-gram oral glucose tolerance test, though current consensus holds that IGF-1 above 1.3 times the age-specific upper limit confirms the diagnosis in a patient with typical features. Springer

• Low IGF-1 alone does not diagnose adult growth hormone deficiency. AACE and ACE guidance is explicit that random GH and IGF-1 levels cannot be used alone to diagnose adult GHD; stimulation testing is required. Medscape

• Expect natural variation. In healthy volunteers tested twice two weeks apart, 46 of 84 participants varied by more than 10%, 12 varied by more than 20%, and 5 varied by more than 30%. Oxford Academic

What IGF-1 Actually Measures

Your pituitary releases growth hormone in bursts, mostly during deep sleep. GH travels to the liver, and the liver responds by producing IGF-1, which carries out most of GH's downstream effects on muscle, bone, and connective tissue.

The practical difference between the two is half-life. Uncomplexed IGF-1 clears in about 10 minutes, but the IGFBP-3/IGF-1 complex is cleared with a half-life of roughly 12 hours. That buffering is why a single IGF-1 draw is informative and a single random GH draw usually is not. Measure GH at 3 p.m. and you may catch a trough that looks like deficiency. Measure IGF-1 at 3 p.m. and you get a rough average of the last day or so of GH activity. Mayo Clinic Laboratories

This is also why the GH-IGF-1 axis is tied so closely to sleep. In Van Cauter's 2000 JAMA study of healthy men, deep slow-wave sleep fell from a mean of 18.9% of the night in men aged 16 to 25 to 3.4% by midlife (ages 36 to 50), and GH secretion was significantly associated with slow-wave sleep independently of age. ResearchGatePubMed

IGF-1 is not a testosterone test

Worth stating plainly, because the two get conflated constantly in men's health marketing. IGF-1 reflects growth hormone activity. Total and free testosterone reflect gonadal function. They are different axes, they can move independently, and one does not substitute for the other. If you want a picture of both, you order both.

How to Test Your IGF-1: Step by Step

Short answer: To test your IGF-1, order a serum insulin-like growth factor 1 test (CPT 84305) either through your clinician or a direct-to-consumer lab service, stop biotin supplements at least 12 to 72 hours beforehand depending on the lab's instructions, give a single morning blood draw, and ask for the result to include an age- and sex-adjusted Z-score. Fasting is usually not required, but keeping your conditions consistent between draws matters more than fasting itself.

The full process:

1. Decide how you are ordering it. Through a physician, IGF-1 is often covered when there is a documented clinical reason. Cash-pay through a direct-to-consumer service is frequently cheaper if you are self-monitoring, especially on a high-deductible plan.

2. Pick your assay and stick with it. The two common versions are LabCorp's immunoassay (test 010363) and Quest's mass spectrometry version (test 16293, IGF-1 LC/MS). Note that the LabCorp version does not include a Z-score, while the Quest LC/MS version reports male and female Z-scores. Walk-In Lab

3. Stop biotin. This is the single most common way to ruin an IGF-1 result. Check your multivitamin, your hair-skin-nails supplement, and your pre-workout.

4. Book a morning draw. Not because IGF-1 swings much during the day, but because standardizing the conditions is what makes your next test comparable to this one.

5. Give the lab your age and sex. Mayo Clinic Laboratories lists this as necessary information, and ARUP requires both to calculate a Z-score. Without them you get a number with no context. Mayo Clinic LaboratoriesARUP Laboratories

6. Add the tests that make the result interpretable. TSH, a liver panel, fasting glucose or A1c, and a CBC at minimum. More on why below.

7. Do not act on one value. If the result does not match your clinical picture, repeat it. Clemmons and Bidlingmaier specifically recommend repeating IGF-1 results that do not fit the patient's picture, using a laboratory with adequate reference ranges and a low coefficient of variation. Oxford Academic

Do you need to fast for an IGF-1 test?

Usually not. Most labs list no fasting requirement, and Testing.com notes that no preparation is generally needed unless you are specifically instructed otherwise. Some clinicians still prefer a fasting morning draw purely for consistency. Both approaches are defensible. What is not defensible is a fasting baseline followed by a fed retest, then treating the difference as a real change. Testing.com

What an IGF-1 test costs

Advertised direct-to-consumer prices ranged from about $19 to $139 as of mid-2026, before a one-time draw fee. Most of these services route samples to the same national reference labs, usually Labcorp or Quest, so a low price does not necessarily mean a lower-quality measurement. Confirm current pricing before ordering, since these change often. Mito HealthMito Health

What the Number Means

Your reference range moves with your age

IGF-1 declines immediately after birth, rises to a pubertal peak around age 15, and then decreases continuously across the rest of life. That means a 250 ng/mL result is unremarkable at 22 and clearly elevated at 60. PubMed

Here are the adult male intervals published by Mayo Clinic Laboratories for its chemiluminescence IGF-1 assay, to illustrate the shape of that decline:

Two cautions on that table. First, female intervals are different and generally lower in adulthood. Second, and more importantly, these are assay-specific. Mayo states directly that IGF-1 assays exhibit variability among platforms and manufacturers, and that results from different methods or kits should not be used interchangeably. Use your own lab's range, not this one. Mayo Clinic Laboratories

Ask for the Z-score

A Z-score expresses how far your result sits from the mean for people your age and sex, in standard deviations. Results within the reference interval have a Z-score between -2.0 and +2.0. A Z above +2.0 suggests GH excess; a very low Z raises the question of deficiency. ARUP LaboratoriesHealthMatters.io

This is the number to track. Your raw value will drift downward over the years simply because you are getting older. Your Z-score will not, unless something has actually changed.

One honest limitation: Z-scores do not fully solve the cross-lab problem. In a comparison of six commercial immunoassays, two showed good agreement after SDS conversion, but two others showed discrepancies wide enough that the correction did not resolve the problem. Oxford Academic

There is no established "optimal" IGF-1 for healthy adults

This is where a lot of online content overreaches. A reference interval describes what is statistically typical. It is not a target you should be optimizing toward.

The observational data are genuinely U-shaped. A 2022 meta-analysis in Aging Cell pooled 19 prospective cohorts and 30,876 participants and found a U-shaped dose-response relation, with both low versus middle (HR 1.33) and high versus middle (HR 1.23) IGF-1 associated with increased all-cause mortality, and a 120 to 160 ng/mL range associated with the lowest mortality. That is interesting. It is also observational, assay-dependent, and not a clinical target. The authors themselves noted that it is unclear which range below 120 ng/mL carries the increased risk, and that populations below that threshold may be heterogeneous. ResearchGate

Treat it as background context, not a goal.

What a High IGF-1 Result Means

Persistently elevated IGF-1 for your age is the standard screening signal for growth hormone excess, which causes gigantism before growth plates close and acromegaly after. Mayo notes that elevated IGF-1 supports a diagnosis of acromegaly or gigantism in individuals with appropriate symptoms or signs. Mayo Clinic Laboratories

Symptoms worth mentioning to a physician alongside a high result include enlarging hands or feet, ring or shoe size changes, jaw or brow changes, new headaches, new snoring or sleep apnea, and joint pain.

Confirmation is a clinician's job. Investigation of GH suppression during a 75-gram, two-hour oral glucose tolerance test is the recommended confirmatory test for cases with elevated age- and sex-adjusted IGF-1, and the 14th Acromegaly Consensus Conference concluded that in a patient with typical features, IGF-1 above 1.3 times the age-specific upper limit confirms the diagnosis without further testing. nihSpringer

A single mildly high value in someone with no symptoms is most often assay variation or biological noise. It warrants a repeat, not alarm.

What a Low IGF-1 Result Means

Here is where most people go wrong. A low IGF-1 does not mean you have a pituitary problem, and it does not mean you need growth hormone.

Because normal serum IGF-1 is so frequently found in hypopituitary adults with genuine GH deficiency, it is widely accepted that adults clinically suspected of GHD must undergo GH provocative testing to confirm the diagnosis. AACE and ACE guidance states that random serum GH and IGF-1 levels cannot be used alone to diagnose adult GHD, and recommends the insulin tolerance test to establish it. There is one narrow exception: AACE allows continuation without provocative testing when there is biochemical evidence of three or more pituitary hormone deficiencies together with IGF-1 below -2.0 SD score. Glucagon Stimulation Testing in Assessing for Adult Growth Hormone Deficiency: Current Status and Future Perspectives +2

Things that lower IGF-1 before you blame your pituitary

• Underfeeding and calorie restriction. Malnutrition produces low IGF-1 that recovers with restored nutrition. Systematic review data show an inverse correlation between energy intake and plasma IGF-1. If you tested in the middle of an aggressive cut, that is your answer. Mayo Clinic LaboratoriesScienceDirect

• Low protein intake. Same mechanism, independent contribution.

• Hypothyroidism, which reduces hepatic responsiveness to GH.

• Chronic liver disease. IGF-1 is made in the liver, so hepatic dysfunction lowers output independent of pituitary function.

• Poorly controlled diabetes, which creates hepatic GH resistance.

• Chronic kidney disease and systemic inflammation.

• Glucocorticoids, whether prescribed or from a long steroid course.

• Oral estrogen, which suppresses hepatic IGF-1 production through first-pass effects in a way transdermal routes largely avoid. This is significant enough that oral estrogen is discontinued for at least four weeks before an OGTT for acromegaly to avoid inaccurate results. Rare Disease Advisor

• Acute illness. Test when you are well.

• High-dose biotin, which is an assay artifact rather than a real change.

Excess body weight complicates the picture rather than simply lowering the number. Obesity blunts both spontaneous and stimulated GH secretion, amounting to a state of relative GH deficiency, yet total and bioactive IGF-1 are relatively preserved despite those reduced GH levels. In other words, a normal IGF-1 in someone carrying significant excess weight does not confirm a healthy GH axis. Frontiers

Why Two Labs Can Give You Two Different Numbers

If you take nothing else from this, take this: do not compare an IGF-1 from one lab to an IGF-1 from another and treat the difference as a physiological change.

Three separate sources of noise stack up.

Assay bias between platforms. A French laboratory comparing standard curves from six commercial immunoassays found markedly different absolute IGF-1 values. Even mass spectrometry does not fully solve it. Adopting a central calibrator across laboratories reduced between-laboratory variability to 6.9%, compared with 19% using a local calibrator. Oxford AcademicOxford Academic

Reagent lot drift. Comparison of 32 lots of pure standard distributed with assay kits over five years showed a high degree of variability that would have affected reported results regardless of how carefully individual labs ran the assay. Oxford Academic

Real biological variation. In 84 healthy volunteers tested at baseline and two weeks later, 46 varied by more than 10%, 12 by more than 20%, and 5 by more than 30%. The contributors include puberty, pregnancy, changes in energy or protein intake, intensive exercise, and stress. Oxford Academic

There is even a geographic wrinkle. A comparison of normative data from more than 1.4 million patients in European countries and the United States found the upper limit of normal was 15% to 20% higher for US residents. Oxford Academic

Practical takeaway: same lab, same assay, same conditions, every time. The 2014 Endocrine Society acromegaly guideline suggests maintaining the same GH and IGF-1 assay in the same patient throughout management, and the same logic applies to anyone tracking themselves. Oxford Academic

Tests That Belong Alongside IGF-1

IGF-1 in isolation is a number without a story. These make it interpretable.

Where BioPro+ Fits, and Where It Does Not

BioPro+ from BioProtein Technology is a drug-free, non-synthetic sublingual liquid built around a proprietary elk antler velvet extract, shilajit, and functional botanicals including aloe vera, goji, and tribulus. It is a dietary supplement designed to support the body's own physiological processes rather than override them, taken under the tongue instead of injected, with no prescription and no needles. It is third-party tested, and BioProtein Technology publishes its full ingredient-level research base rather than gesturing vaguely at "clinical studies."

Now the part that most supplement content will not tell you: do not use an IGF-1 blood test as your yardstick for evaluating a supplement.

The best-controlled human trial of oral antler velvet remains Sleivert and colleagues in the International Journal of Sport Nutrition and Exercise Metabolism (2003). Thirty-eight active males were randomly assigned in double-blind fashion to deer antler velvet extract, powder, or placebo, and tested before and after a 10-week strength program with measurement of testosterone, insulin-like growth factor, erythropoietin, red cell mass, plasma volume, and total blood volume. There were no endocrine, red cell mass, or VO2max changes in any group. A more recent controlled trial of seven-day sublingual supplementation also did not identify an increase in IGF-1 between the antler velvet and placebo groups. PubMedUniversity of Nevada, Las Vegas

That is the honest state of the evidence, and it is why BioPro+ is positioned around system support and how you look, perform, and feel, not around moving a specific lab value. Oral peptides and growth factors face a straightforward obstacle: the digestive tract. A supplement that respects that reality and does not promise to raise your serum IGF-1 is being straight with you. Judge it on how you actually function over weeks and months, and on whatever labs your clinician recommends for your specific situation.

If you want a genuine baseline, get your IGF-1 and the supporting panel above drawn before you start anything new, whether that is a supplement, a training block, or a diet change. Baselines are only useful if you take them first.

These statements have not been evaluated by the Food and Drug Administration. BioPro+ is not intended to diagnose, treat, cure, or prevent any disease.

How Often Should You Retest?

There is no consensus interval for healthy adults, because IGF-1 is not a recommended routine screening test in people without symptoms or known pituitary disease.

If you are testing out of curiosity or for personal tracking, an annual draw under identical conditions gives you a trend without over-reading noise. Retest sooner if you have made a substantial change to protein intake, body weight, training volume, or thyroid medication, since all of those genuinely move the number.

If you are being monitored for a known pituitary condition or on GH-axis therapy, your endocrinologist sets the schedule. For context on why patience is warranted: stabilization of IGF-1 values can take as long as 12 weeks after pituitary surgery. Oxford Academic

Common Mistakes When Testing IGF-1

• Taking a biotin-containing supplement in the days before the draw

• Comparing results from two different labs or two different assays

• Using an adult "normal range" pulled off the internet instead of your own lab's age- and sex-specific interval

• Testing during an aggressive calorie deficit or an acute illness, then treating the low result as a hormonal diagnosis

• Interpreting a low IGF-1 as proof of growth hormone deficiency

• Acting on a single value without repeating it

• Skipping TSH and a liver panel, then having no way to explain an unexpected result

• Expecting a supplement to change the number

The Bottom Line

IGF-1 is a good test that gets read badly. It is a stable, single-draw proxy for average growth hormone activity, it is cheap and widely available, and it is genuinely useful as a screening tool for GH excess and as part of a workup for GH deficiency.

What it is not is a scorecard. It is not a target to optimize, it is not interchangeable across labs, and it does not diagnose anything on its own.

Your next steps:

1. Order an IGF-1 test through your clinician or a direct-to-consumer service, and add TSH, a liver panel, and fasting glucose or A1c to the same draw.

2. Stop biotin supplements beforehand and note the exact lab and assay used.

3. Ask for the age- and sex-adjusted Z-score, not just the raw value.

4. Bring anything outside the reference interval to a physician rather than self-interpreting it, and be prepared to repeat the test.

5. Use the same lab under the same conditions for every future draw.

Frequently Asked Questions

Do I need to fast for an IGF-1 blood test?

Generally no. Most laboratories do not require fasting for IGF-1, because levels do not swing sharply with meals the way glucose or insulin do. What matters far more is consistency. If your baseline was a fasting morning draw, make your follow-ups fasting morning draws too. Follow your specific lab's written instructions, and stop biotin-containing supplements beforehand, since biotin can make IGF-1 results falsely low.

What is a normal IGF-1 level for a man over 40?

It depends on both your exact age and the assay your lab uses. As an illustration, Mayo Clinic Laboratories publishes intervals of roughly 74.9 to 216.4 ng/mL for men aged 41 to 45 and 66.9 to 205.1 ng/mL for men aged 46 to 50 with its chemiluminescence assay. Other platforms produce different absolute numbers for the same sample, so always read your result against your own lab's stated range. The Z-score is a more portable measure: inside the reference interval corresponds to a Z between -2.0 and +2.0.

Does a low IGF-1 mean I have growth hormone deficiency?

No. Nutrition, thyroid status, liver function, glycemic control, inflammation, glucocorticoids, oral estrogen, and normal aging all lower IGF-1. AACE and ACE guidance is explicit that random GH and IGF-1 levels cannot diagnose adult growth hormone deficiency on their own, and that GH stimulation testing is required in nearly all cases. Conversely, many adults with genuine GH deficiency have a normal IGF-1, which is exactly why provocative testing exists.

Can a supplement raise my IGF-1 level?

There is no good human evidence that oral supplements meaningfully raise serum IGF-1. In a 10-week randomized, double-blind trial of 38 active men, deer antler velvet extract and powder produced no endocrine changes compared with placebo, and a separate controlled trial of sublingual supplementation found no IGF-1 difference versus placebo either. BioPro+ is positioned accordingly, as system-level support for how you look, perform, and feel rather than as something that changes a lab number. Be skeptical of any product marketed on the promise of raising your IGF-1.

Is IGF-1 banned in sports?

Exogenous IGF-1 is prohibited. WADA lists insulin-like growth factor 1 (mecasermin) and its analogues under section S2.3 of the Prohibited List, banned at all times, both in-competition and out-of-competition. Separately, WADA has stated that very small quantities of IGF-1 occur naturally in animal products such as colostrum and deer antler velvet, and repeats its warning that athletes who use these types of products do so at their own risk. If you compete under an anti-doping program, clear any antler-derived product with your governing body before using it. The Prohibited List | World Anti Doping Agency +2

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These statements have not been evaluated by the Food and Drug Administration. BioPro+ is not intended to diagnose, treat, cure, or prevent any disease. This content is for informational purposes only and is not a substitute for medical evaluation, diagnosis, or treatment. Talk to a licensed clinician about your individual situation and before interpreting or acting on any lab result.