An IGF-1 blood test and a growth hormone test are not the same thing.
Growth hormone, or GH, is released from the pituitary gland in pulses. Its concentration can rise sharply and then fall to very low levels within the same day. That makes a random GH result difficult to interpret.
IGF-1 behaves differently. Insulin-like growth factor 1 is produced mainly by the liver in response to growth hormone and remains much more stable in the bloodstream.
Growth hormone can change dramatically from moment to moment. IGF-1 reflects integrated growth-hormone activity more consistently over time.
That does not make IGF-1 definitive on its own. Age, nutrition, liver function, kidney function, pregnancy, medicines and other clinical factors can all affect interpretation.
IGF-1 vs Growth Hormone at a glance
Feature | IGF-1 | Growth Hormone |
Main source | Produced mainly by the liver and other tissues in response to GH | Produced by the pituitary gland |
Secretion pattern | Relatively stable | Pulsatile and highly variable |
Random blood measurement | Usually clinically interpretable | Often difficult to interpret |
Suspected acromegaly | Preferred first-line biochemical test | Dynamic suppression testing may be used when needed |
Suspected GH deficiency | Can support assessment | Stimulation testing is often required |
Interpretation | Strongly age-dependent | Depends heavily on timing and physiological context |
Fasting | Usually not required when tested alone | Depends on the type of GH test |
Lab Tests Online UK explains that IGF-1 is useful because it reflects average GH activity more consistently than growth hormone itself.
What is igf 1?
IGF-1 stands for insulin-like growth factor 1. It is produced mainly by the liver following stimulation by growth hormone.
Pituitary gland ? Growth hormone ? Liver and tissues ? IGF-1
IGF-1 helps mediate many of growth hormone's effects on bone and tissue growth, protein synthesis, muscle and tissue development, metabolism and cell growth.
Despite its name, igf-1 is not simply an insulin test.
Why is a random growth hormone test difficult to interpret?
Growth hormone is secreted in bursts. Levels can rise during sleep, exercise and other physiological stimuli, then fall very low between pulses.
A low random result may simply have been taken between GH pulses, while a higher result may have been collected during one.
When actual GH secretion needs to be assessed, endocrinologists usually use dynamic testing, where growth hormone is measured in response to a controlled stimulus or suppression test.
Why is an igf 1 blood test usually more useful?
IGF-1 changes far less over short periods. That gives a single blood sample considerably more interpretive value than a random GH measurement.
An igf 1 blood test may be used in suspected acromegaly, pituitary disease, possible GH deficiency, monitoring established acromegaly, monitoring prescribed growth hormone therapy and evaluation of growth disorders in children.
It is not a general “growth hormone score” or a routine test of fitness, muscle gain, recovery or biological age.
Why does age matter so much for IGF-1?
Age is essential to interpretation. IGF-1 concentrations rise during childhood, increase substantially during puberty and adolescence, and then gradually decline through adulthood.
The same IGF-1 concentration can have a completely different meaning in two people of different ages.
A result should always be interpreted against the age-adjusted reference interval supplied by the laboratory.
Mayo Clinic Laboratories emphasises that IGF-1 reference ranges vary substantially with age.
Can IGF-1 results from different laboratories be compared?
Cautiously. Different laboratories may use different analysers, assay methods and reference intervals. A raw IGF-1 number from one laboratory is not always directly interchangeable with a result from another.
Where serial monitoring is important, using the same laboratory and assay method where practical can make trends easier to interpret.
Why is an igf 1 test used for suspected acromegaly?
Acromegaly is caused by prolonged excessive growth hormone activity, most commonly from a benign GH-secreting pituitary tumour.
Growth hormone stimulates IGF-1 production, so sustained GH excess usually leads to an elevated age-adjusted IGF-1 concentration. That makes IGF-1 the preferred first-line biochemical marker when acromegaly is suspected.
Current international consensus supports using age-adjusted IGF-1 as the primary biochemical test. In someone with typical clinical features, a clearly elevated result may provide strong evidence of the diagnosis, while borderline or discordant results may require repeat testing or additional dynamic assessment. Read the international consensus.
Does high IGF-1 mean acromegaly?
Not automatically. An elevated result needs to be interpreted against age, the laboratory reference interval, clinical features, pregnancy, liver function, kidney function, diabetes control, nutritional status, oestrogen treatment and assay method.
If an IGF-1 result is unexpectedly high but the clinical picture does not fit, repeating the test may sometimes be appropriate.
When is a glucose suppression test used?
Growth hormone normally falls after a glucose load. In acromegaly, GH suppression may be impaired.
An oral glucose tolerance test with serial GH measurements can therefore be used when the diagnosis remains uncertain, particularly with borderline or discordant IGF-1 results.
What symptoms can occur with acromegaly?
Possible features include increasing shoe or ring size, enlarged hands or feet, coarsening facial features, a more prominent jaw, increased sweating, headaches, joint pain, carpal tunnel symptoms, sleep apnoea, menstrual changes, erectile difficulties and visual symptoms in some people with larger pituitary tumours.
The NHS notes that the changes can develop gradually.
Does low igf 1 mean growth hormone deficiency?
No. Growth hormone deficiency is one possible explanation, but significant calorie restriction, malnutrition, chronic liver disease, chronic kidney disease, systemic illness, GH resistance, some hormonal treatments and normal age-related decline can also lower IGF-1.
Can normal IGF-1 rule out growth hormone deficiency?
Not in every patient. A normal result may make severe GH deficiency less likely in some clinical situations, but it does not universally exclude it.
Adult GH deficiency is usually investigated in a relevant context such as known pituitary disease, pituitary surgery, cranial radiotherapy, structural hypothalamic or pituitary abnormalities or deficiencies of other pituitary hormones.
The Endocrine Society recommends stimulation testing in most adults where confirmation of GH deficiency is required.
How is growth hormone deficiency tested?
Unlike IGF-1 testing, diagnosis of GH deficiency often requires a dynamic test that assesses whether the pituitary can release growth hormone appropriately in response to a controlled stimulus.
This is why ordering a random growth hormone test and finding a low result does not establish GH deficiency.
How does IGF-1 testing differ in children and adults?
In children
IGF-1 may contribute to investigation of poor growth velocity, short stature, suspected GH deficiency, possible GH excess and certain growth disorders.
In adults
IGF-1 is more commonly used in suspected acromegaly, known pituitary disease, suspected adult GH deficiency, monitoring GH-related disorders and monitoring prescribed GH therapy.
Can diet or illness alter an igf test?
Yes. Significant calorie restriction or malnutrition can lower IGF-1. Liver disease can reduce IGF-1 production because the liver is the main source of circulating IGF-1. Kidney disease and poorly controlled diabetes can also complicate interpretation.
Pregnancy changes IGF-1 physiology and requires separate interpretation. Oral oestrogen can also alter the GH–IGF-1 relationship.
Can supplements interfere with IGF-1 testing?
Possibly. High-dose biotin can interfere with some laboratory immunoassays, including certain IGF-1 methods. If you take supplements containing large amounts of biotin, tell the laboratory or clinician before testing.
Is IGF-1 a muscle, recovery or anti-ageing score?
No. IGF-1 has genuine biological effects on growth, tissue development and metabolism, but a higher IGF-1 result is not automatically “better”.
Clinical testing is not intended to rank muscle-building potential, exercise recovery, biological age, longevity or general wellness.
An IGF-1 blood test should therefore be treated as an endocrine marker, not a wellness score.
Is IGF-1 a cancer screening test?
No. The IGF system has been studied in cancer biology, but clinical IGF-1 measurement is not a validated cancer-screening test.
Does an igf 1 blood test require fasting?
Usually not when IGF-1 is measured on its own. Strict morning timing is also not normally required for an isolated measurement.
Preparation may differ if IGF-1 is included with glucose, insulin or other tests requiring fasting.
IGF-1 or Growth Hormone: which test answers which question?
Clinical question | More useful approach |
Suspected acromegaly | Age-adjusted IGF-1 |
Borderline or uncertain acromegaly assessment | Repeat IGF-1 and/or GH suppression testing where appropriate |
Suspected adult GH deficiency | IGF-1 can support assessment, but stimulation testing may be required |
Monitoring established acromegaly | IGF-1 alongside specialist follow-up |
Monitoring prescribed GH treatment | IGF-1 |
Random curiosity about a “GH level” | Random GH is often difficult to interpret |
The test needs to match the clinical question.
IGF-1 Testing at London Blood Tests
London Blood Tests offers a standalone IGF-1 (Somatomedin) Blood Test.
Test detail | Current information |
Biomarker | IGF-1 (Somatomedin) |
Current price | £140.99 |
Typical turnaround | 1 business day |
Sample | Venous blood |
Biomarkers | 1 |
Collection | Clinic or eligible home visit |
The test measures IGF-1 rather than a random growth hormone concentration.
Booking an IGF-1 Blood Test in London
Private IGF-1 testing is available through London Blood Tests at participating clinics and through eligible home collection.
Before booking, check whether your clinician specifically requested IGF-1 or Growth Hormone. They are not interchangeable.
If you have previous IGF-1 results, keep the full reports because reference intervals and assay methods can differ between laboratories.
Our Private Blood Tests in London guide explains private appointment and blood-collection options.
Frequently Asked Questions
Is igf-1 the same as growth hormone?
No. Growth hormone is produced by the pituitary gland. IGF-1 is produced mainly in response to growth hormone and mediates many of GH's effects.
Why is an igf 1 test more useful than random GH?
Growth hormone is released in pulses and can change dramatically over short periods. IGF-1 is more stable and therefore provides a more integrated indication of GH activity.
Does high igf 1 confirm acromegaly?
Not by itself in every situation. Clearly elevated age-adjusted IGF-1 together with typical clinical features can strongly support the diagnosis, while borderline or discordant results may require repeat testing or specialist dynamic assessment.
Does low igf-1 mean growth hormone deficiency?
No. GH deficiency is one possible cause, but nutrition, liver disease, kidney disease and other conditions can also lower IGF-1.
Can normal IGF-1 rule out growth hormone deficiency?
Not in every patient. Where genuine GH deficiency is suspected, specialist stimulation testing may still be required.
Can IGF-1 results from different laboratories be compared?
Only cautiously. Assay methods and age-adjusted reference intervals can differ.
How long does igf 1 blood test take at London Blood Tests?
The current listed laboratory turnaround for the standalone IGF-1 (Somatomedin) test is approximately 1 business day.
The Bottom Line
An IGF-1 blood test is usually more useful than a random growth hormone test when the aim is to assess overall activity across the GH–IGF-1 axis.
Growth hormone is released in pulses. IGF-1 is more stable.
But interpretation is not as simple as High = GH excess or Low = GH deficiency. Age-adjusted reference ranges, nutrition, liver and kidney function, pregnancy, medicines and assay method all matter.
Most importantly, IGF-1 should be viewed as an endocrine marker—not a score of muscle growth, recovery, anti-ageing or general wellness.
London Blood Tests offers a standalone IGF-1 (Somatomedin) Blood Test, currently listed at £140.99 with an expected turnaround of approximately one business day.