An IGF-1 blood test measures insulin-like growth factor 1 in serum to track overall growth hormone activity. At Longevity Benchmark, we evaluate endocrine assays and reference laboratory protocols to help readers navigate clinical testing. Pituitary growth hormone spikes and clears within minutes. That volatility makes random growth hormone measurements clinically unhelpful. In contrast, IGF-1 binds to carrier proteins that maintain steady blood concentrations throughout the day.
The Verdict
Biological Structure and Origin of Somatomedin C
Insulin-like growth factor 1 is a 70-amino-acid peptide hormone produced primarily by the liver in response to pituitary growth hormone stimulation. Documentation from Labcorp identifies the molecule as a small peptide with a molecular weight of 7647. The hormone shares roughly 50% sequence homology with proinsulin and exhibits biological actions similar to insulin, influencing glucose uptake and protein synthesis.
The hormone was originally designated somatomedin C because it mediates the somatic growth effects stimulated by growth hormone. Older clinical reports, archived hospital records, and laboratory directories frequently list the synonym SM-C/IGF-1 or categorize the assay under CPT code 84305 as an assay of somatomedin. IGF-1 stimulates muscle development, bone mineralization, and tissue remodeling throughout life. Because of its metabolic influence, researchers often examine how the peptide interacts with markers such as fasting insulin.
In the bloodstream, IGF-1 does not circulate as a free peptide in meaningful amounts. Almost 100% of circulating IGF-1 binds to high-affinity IGF-binding proteins, with IGF-binding protein 3 (IGFBP-3) being the most abundant carrier. These binding proteins protect the peptide from rapid degradation, prevent unexpected drops in blood sugar, and maintain a large circulating reservoir. Blood concentrations begin at low levels in infancy, climb steadily through childhood, reach an absolute peak during the adolescent growth spurt, and decline continuously throughout adulthood.
Growth Hormone Secretion Dynamics Versus IGF-1 Stability
Direct growth hormone testing is clinically unreliable because the pituitary gland releases the hormone in short, erratic bursts throughout the day. Clinical guidance from Labcorp notes that an isolated fasting growth hormone measurement carries limited clinical value. Growth hormone secretion is episodic and pulsatile, exhibiting a brief circulatory half-life of only 20 to 25 minutes. Levels surge unpredictably during physical exercise, deep sleep onset, and acute drops in circulating glucose.
Because of these rapid pulses, a blood draw taken twenty minutes apart in the same patient can produce wildly disparate growth hormone values. The National Institute of Diabetes and Digestive and Kidney Diseases points out that measuring IGF-1 provides a dependable way to track growth hormone activity because circulating levels remain steady throughout waking hours. Free IGF-1 clears quickly, with a half-life of roughly 10 minutes. However, it binds to IGFBP-3 and an acid-labile subunit to form a ternary complex. As documented by Boisclair and colleagues, this ternary complex extends the circulatory half-life of IGF-1 to more than 12 hours.
This biological mechanism turns IGF-1 into a stable, integrated readout of daily growth hormone exposure. In clinical practice guidelines published in the Journal of Clinical Endocrinology and Metabolism, the Endocrine Society recommends IGF-1 as the primary initial test for suspected acromegaly. The guideline authors specifically recommend against relying on random growth hormone levels because episodic secretion generates frequent false negatives and false positives.
Clinical Indications for Growth Hormone Axis Testing
Physicians order an IGF-1 test to evaluate suspected growth hormone excess, adult hormone deficiency, and treatment efficacy during replacement therapy. The most common cause of pathological growth hormone excess is acromegaly, an uncommon endocrine condition. According to NIDDK, acromegaly affects roughly 3 to 14 people per 100,000. More than 9 out of 10 cases stem from a benign pituitary adenoma. The condition is most commonly diagnosed in middle-aged adults, though tissue changes develop gradually over several years.
The Endocrine Society recommends measuring IGF-1 in patients exhibiting typical physical manifestations of acromegaly, particularly enlarged hands, broadened feet, and altered facial features. Their guidelines also suggest testing patients who present with combinations of associated secondary conditions. These include obstructive sleep apnea, type 2 diabetes mellitus, debilitating arthritis, carpal tunnel syndrome, hypertension, and excessive sweating.
Physicians also use the assay to evaluate growth failure in pediatric patients and suspected growth hormone deficiency in adults with hypothalamic-pituitary disease. In therapeutic settings, serial IGF-1 testing allows endocrinologists to titrate recombinant growth hormone dosing or monitor patient response during secretagogue protocols such as sermorelin therapy. The test also assists in monitoring catabolic states and severe nutritional insufficiency.
Diagnostic Limitations Requiring Dynamic Confirmatory Testing
An isolated IGF-1 blood test cannot definitively confirm or exclude a pituitary growth hormone disorder on its own. While an elevated IGF-1 level points toward growth hormone excess, clinical guidelines require confirmatory testing before establishing an acromegaly diagnosis. The Endocrine Society specifies that confirmation requires demonstrating a failure of growth hormone to suppress below 1 microgram per liter during an oral glucose tolerance test. During this confirmatory protocol, the patient drinks a sugary liquid, and a health professional tests the blood every half hour for 2 hours to measure growth hormone levels.
A consensus statement published by Giustina and colleagues notes that an IGF-1 concentration greater than 1.3 times the upper limit of normal for age confirms acromegaly in a patient with classic signs, but ambiguous cases still mandate formal glucose suppression testing. Conversely, a normal IGF-1 level does not rule out adult growth hormone deficiency. Clinical guidelines published by Molitch and colleagues state that a normal IGF-1 makes provocative stimulation testing mandatory unless a patient already has three documented pituitary hormone deficits combined with an IGF-1 below 84 nanograms per milliliter.
Non-pituitary conditions can also distort test results. Labcorp documentation warns that malnutrition causes low somatomedin C concentrations despite normal circulating growth hormone levels. Furthermore, reference intervals vary markedly across age groups and commercial testing platforms. Readers reviewing their own numbers should consult our detailed breakdown of IGF-1 levels by age to understand how intervals shift across decades, or review our guide on normal versus optimal reference ranges to understand clinical thresholds.
An IGF-1 blood test is not an effective screening tool for healthy adults seeking an unguided longevity score. Healthy individuals looking for general metabolic risk markers should prioritize fasting insulin and standard glycemic measures before evaluating pituitary hormone pathways.
IGF-1 Blood Test Requirements Across Reference Laboratories
Clinical testing for IGF-1 requires venous serum collected in additive-free or separator tubes, as plasma specimens are rejected by major reference laboratories. Serum must be promptly separated from red blood cells via centrifugation and placed into plastic transport tubes to prevent cellular metabolism from altering peptide stability.
Collection manuals from reference laboratories emphasize that requisition forms must include the patient's chronological age. Because circulating IGF-1 concentrations decline by more than 70% between adolescence and late adulthood, a raw numerical value in nanograms per milliliter is uninterpretable without an age-stratified reference interval. Laboratories such as ARUP Laboratories also require patient biological sex to calculate a standard deviation z-score.
| Laboratory | Test Code and Method | Sample and Container | Specimen Volume | Sample Stability | Specimen Rejection Criteria |
|---|---|---|---|---|---|
| Labcorp | Test 010363, Immunochemiluminometric assay (ICMA, IDS-iSYS) | Serum, Red-top tube or gel-barrier tube (SST) | 0.5 mL (0.2 mL minimum) | Room temperature 3 days, refrigerated 7 days, frozen 90 days | Plasma specimens |
| ARUP Laboratories | Test 2007698, Quantitative chemiluminescent immunoassay (CLIA) | Serum, Serum Separator Tube (SST) | 1.0 mL (0.5 mL minimum) | Ambient 24 hours, refrigerated 1 week, frozen 1 year | Plasma, tissue, urine, gross hemolysis, gross lipemia |
| Quest Diagnostics | Test 16293, Liquid Chromatography and Mass Spectrometry (LC/MS) | Serum, Red-top tube (no additive) or SST | 0.5 mL (0.3 mL minimum) | Room temperature 48 hours, refrigerated 5 days, frozen 28 days | Plasma, gross hemolysis, gross lipemia, icterus |
Fasting Guidelines and Acute Caloric Deprivation
Standard reference laboratories list no mandatory fasting requirement for an IGF-1 blood test. Test directories published by Labcorp and ARUP Laboratories contain no fasting instructions, and consumer collection protocols through Labcorp OnDemand do not instruct patients to fast overnight. Patients can undergo phlebotomy in a fed or unfed state without altering clinical interpretation.
However, there is a clear distinction between standard overnight fasting and prolonged nutritional deprivation. While skipping a single meal has no measurable effect on circulating somatomedin C, extended caloric restriction suppresses hepatic IGF-1 synthesis. In a landmark clinical study published in the Journal of Clinical Endocrinology and Metabolism, Bang and colleagues demonstrated that 4 days of total fasting produced a 37% decrease in serum IGF-1 concentrations in healthy non-obese adults. In obese participants, the decline was delayed, reaching a 23% reduction after 4 days.
Consequently, individuals undergoing extended water fasts or following an aggressive fasting protocol can expect their measured IGF-1 levels to drop temporarily below their personal baseline. When scheduling an IGF-1 draw to evaluate baseline endocrine health, complete the test during a period of typical dietary intake. If your physician pairs the order with fasting glucose, insulin, or lipid panels, you must follow the overnight fasting protocol required for those companion assays.
Turnaround Times and Retail Laboratory Testing Costs
Turnaround times for an IGF-1 blood test range from one to four business days depending on laboratory logistics and assay methodology. Labcorp reports routine ICMA results for test 010363 within 2 to 4 days, while their calculated z-score test 010540 typically reports within 1 to 3 days. ARUP Laboratories processes samples seven days a week and reports CLIA results within 1 to 2 days of sample receipt. Liquid chromatography-mass spectrometry testing at Quest Diagnostics requires 1 to 4 days.
Consumers who wish to order an IGF-1 test directly without visiting a doctor can purchase an individual assay through Labcorp OnDemand for $139 (checked September 2026). The purchase price covers physician network oversight, specimen processing, and online result delivery through their patient portal. The fee qualifies for reimbursement using health savings accounts (HSA) and flexible spending accounts (FSA).
Commercial direct-to-consumer lab resellers also market requisition orders fulfilled at Quest Diagnostics or Labcorp draw stations, often advertising lower out-of-pocket prices. However, these promotional prices change frequently across independent storefronts. If a physician orders the test for a suspected endocrine condition, commercial health insurance policies generally cover the fee under CPT code 84305, subject to annual deductibles and office copayments. Readers can explore related testing options in our biomarkers directory.
Venous Serum Collection Versus Filter Paper Blood Spots
Venous blood draws processed for serum remain the recognized clinical standard for quantifying circulating IGF-1. Direct-to-consumer tests from Labcorp OnDemand require an in-person visit to a local patient service center where a phlebotomist draws whole blood from an arm vein. Standard laboratory analyzers require between 0.2 mL and 1.0 mL of serum to separate the peptide from binding proteins and run duplicate measurements.
Dried blood spot tests collected via fingerstick at home represent an alternative collection format. Technical documentation from ZRT Laboratory explains that IGF-1 remains stable in whole blood dried on filter paper, permitting room-temperature mailing to a processing facility. Dried blood spot testing offers logistical convenience for remote patients who cannot visit a traditional drawing center.
However, commercial blood spot providers do not publish direct correlation statistics, regression equations, or validation studies comparing capillary blood spot values to gold-standard venous serum immunoassays. Because capillary blood contains interstitial fluid and whole cell lysates, drying dynamics can alter peptide extraction efficiency. All established clinical guidelines, diagnostic thresholds, and published reference ranges stem entirely from venous serum studies. Patients evaluating potential growth hormone disorders should rely on venous phlebotomy.
Biological Confounders and Retest Variability
Circulating IGF-1 concentrations fluctuate in response to systemic illness, hormonal therapies, nutritional intake, and normal biological variation. Because the liver synthesizes IGF-1, chronic liver disease lowers peptide output regardless of pituitary stimulation. Poorly controlled type 2 diabetes, chronic kidney disease, and thyroid disorders also disrupt normal circulating levels. Pregnancy naturally elevates IGF-1 concentrations as the placenta secretes variant growth hormones.
Exogenous medications change circulating levels. Oral estrogen therapy and estrogen-containing birth control pills suppress hepatic IGF-1 synthesis by delivering a high first-pass hormone load to the liver. Transdermal estrogen does not produce this pronounced hepatic suppression. Other endocrine medications, including thyroxine, glucocorticoids, and anabolic steroids, also alter circulating concentrations. Body composition plays a bidirectional role: in underweight and normal-weight individuals, IGF-1 increases as body mass index rises. Conversely, in individuals with severe obesity and visceral adiposity, IGF-1 levels decline as body mass index climbs.
Dietary supplements introduce acute assay interference. Labcorp warns that high doses of biotin (vitamin B7, vitamin B8, or vitamin H) cross-react with the streptavidin-biotin technology used in many automated immunoassays, generating falsely altered readings. Patients must discontinue biotin-containing supplements for at least 72 hours prior to phlebotomy to ensure assay accuracy.
Even in healthy individuals, biological levels vary from week to week. In an investigation published in the European Journal of Endocrinology, Clemmons and Bidlingmaier evaluated 84 healthy adult volunteers across two draws spaced two weeks apart. Among these healthy participants, 46 of 84 had serum IGF-1 values that varied by more than 10%, 12 participants varied by more than 20%, and 5 varied by more than 30%.
Our view on routine testing would change if inter-assay discrepancies between major commercial platforms were resolved and large-scale intervention trials demonstrated that titrating diet or therapy to specific IGF-1 targets in healthy adults improves healthspan. Review any unexpected igf 1 blood test result with an endocrinologist who can correlate the number with your clinical history and determine whether provocative hormone testing is warranted.
Frequently Asked Questions
Do you need to fast for an IGF-1 test?
Routine clinical laboratories such as Labcorp and ARUP Laboratories do not require fasting for an IGF-1 blood test. You can eat and drink normally prior to your appointment. However, if your doctor orders IGF-1 as part of a broader metabolic panel that includes fasting glucose or a lipid panel, you must follow the fasting guidelines for those companion tests. While skipping breakfast does not influence your result, severe prolonged calorie restriction does: clinical research demonstrates that four consecutive days of total fasting lowers serum IGF-1 concentrations by 37% in healthy adults. You must also avoid taking biotin supplements for at least 72 hours prior to the draw to prevent laboratory assay interference.
How is an IGF-1 test done?
An IGF-1 test is conducted through a standard venous blood draw, usually performed at an outpatient diagnostic center or hospital laboratory. A phlebotomist draws blood from a vein in your arm into a red-top or gel-barrier serum separator tube. The laboratory spins the sample in a centrifuge to separate the liquid serum from the cellular components, as standard testing protocols require serum and reject plasma specimens. The separated serum is then analyzed using an automated immunoassay or liquid chromatography-mass spectrometry. The blood collection is a single routine venipuncture, and you can resume normal physical activities immediately following the procedure.
What tube color is used for an IGF-1 blood test?
Phlebotomists collect blood for an IGF-1 test using a red-top tube or a mottled red-and-gray gel-barrier tube, commonly known as a serum separator tube (SST). These tubes allow the blood to clot naturally so laboratory technicians can centrifuge the sample and extract pure serum. Both Labcorp and ARUP Laboratories explicitly reject whole blood and plasma specimens collected in anticoagulant tubes, such as purple-top EDTA tubes or green-top heparin tubes. The collection requires between 0.5 mL and 1.0 mL of serum, with an absolute minimum volume of 0.2 mL to 0.3 mL depending on the specific laboratory analyzer.
Can you get an IGF-1 test at home?
Most clinical IGF-1 testing requires an in-person venous blood draw at an accredited diagnostic facility rather than an at-home kit. While commercial laboratories such as ZRT Laboratory offer dried blood spot fingerstick tests using collection filter paper, published data validating the analytical equivalence between dried capillary blood and venous serum remains limited. Major clinical guidelines and diagnostic cutoffs established by the Endocrine Society are calibrated strictly against venous serum assays. If you order an independent consumer test online through Labcorp OnDemand, you still visit a local patient service center in person so a trained professional can perform a standard venous draw.
How much does an IGF-1 blood test cost?
Direct-to-consumer testing through Labcorp OnDemand costs $139 out of pocket (checked September 2026). This retail price includes the laboratory physician order, the phlebotomy collection fee at a local patient service center, and online portal access to your certified laboratory report. Consumers can pay for the test using standard payment cards, flexible spending accounts (FSA), or health savings accounts (HSA). Third-party laboratory testing brokers frequently advertise lower promotional pricing for physician-requisitioned tests at commercial draw sites. If an endocrinologist orders the test to evaluate a diagnosed medical condition, commercial health insurance policies often cover the cost under CPT code 84305, subject to your copayment or deductible.
Can you order an IGF-1 test yourself?
You can order an IGF-1 test independently in most US states without an initial visit to your primary care physician. Direct-to-consumer platforms such as Labcorp OnDemand partner with licensed physician networks that authorize the laboratory requisition digitally. Once you purchase the order online, you schedule an appointment at a nearby laboratory collection center for a standard blood draw. However, self-ordered results arrive without clinical interpretation. Because IGF-1 reference ranges vary dramatically based on your exact age, biological sex, and the specific assay technology used by the testing facility, you should share your laboratory report with a physician to evaluate what your numbers mean in the context of your overall medical history.
What does an IGF-1 test show?
An IGF-1 test measures the concentration of insulin-like growth factor 1 circulating in your bloodstream, which serves as a stable biological indicator of your body's overall growth hormone production. Because the pituitary gland releases growth hormone in brief, erratic pulses that clear within minutes, measuring direct growth hormone levels in a single draw is rarely helpful. The liver produces IGF-1 in response to growth hormone stimulation, and carrier proteins keep IGF-1 concentrations steady throughout the day. Doctors use the test to investigate pituitary disorders like acromegaly, evaluate adult growth hormone deficiency, assess childhood growth failure, and monitor progress during growth hormone therapy.
How long do IGF-1 test results take?
Laboratory turnaround time for an IGF-1 blood test generally ranges from one to four business days from the moment your blood sample reaches the performing facility. Reference laboratories such as ARUP Laboratories report automated chemiluminescent immunoassay results within one to two days, while Labcorp reports standard immunoassay measurements within two to four days. Quest Diagnostics reports its liquid chromatography-mass spectrometry (LC/MS) test in 1 to 4 days, and Labcorp reports its calculated standard deviation score (z-score) test in 1 to 3 days. Direct-to-consumer services post your final numerical report directly to a secure online portal once laboratory directors verify the findings.