Growth Hormone Unit Converter
Growth Hormone Unit Converter
Convert growth hormone between ng/mL, µg/L, mIU/L and µIU/mL using the WHO standard of 3.0 IU per mg — and see why that factor was different before 2001, and why a single random GH answers almost nothing.
Growth Hormone converter
Mass ⇄ international unitsGrowth hormone 0.8 ng/mL
The four units, and the standard behind the factor of 3
mIU/L = µIU/mL
mIU/L = ng/mL × 3.0
because 1 mg of somatropin = 3.0 IU (WHO International Standard 98/574)
- ng/mL = µg/L
- a nanogram per millilitre and a microgram per litre are the same concentration. Laboratories in the United Kingdom and much of Europe report µg/L; North American reports usually say ng/mL, and the number does not change
- mIU/L = µIU/mL
- also identical to each other. A milli-international-unit per litre is a micro-international-unit per millilitre, for the same reason that ng/mL equals µg/L
- ×3.0, from a potency assignment
- the current WHO International Standard for somatropin, 98/574, is assigned 3.0 International Units per milligram. One microgram per litre therefore carries 3.0 milli-international-units per litre. This is a calibration agreed by collaborative study, not a property of the molecule
- why there is no nmol/L
- the International Unit measures biological potency against a reference preparation, not an amount of substance. Growth hormone circulates as a mixture of the 22 kDa and 20 kDa isoforms and of monomer, dimer and binding-protein-bound forms, so no single molar mass describes what an assay reports. This site carries no molar unit for growth hormone for that reason
- the factor used to be 2.6
- the older International Standard, 80/505, was extracted from human pituitary glands and assigned 4.4 IU per ampoule containing about 1.70 mg of hormone — about 2.59 IU per milligram. A result converted with the old factor and one converted with the new differ by roughly 14%, which is why mIU/L figures in older papers and older reports are not directly comparable with today's
Worked example
Growth hormone 0.8 ng/mL
0.8 ng/mL = 0.80 µg/L — the same number in the other mass convention
0.8 × 3.0 = 2.40 mIU/L = 2.40 µIU/mL, using the current WHO standard 98/574
Converted against the superseded pituitary standard at 2.59 IU/mg, the same sample would have been reported as about 2.07 mIU/L — the same blood, a different number
Going the other way, a historical result of 2.40 mIU/L on the old standard corresponds to 2.40 ÷ 2.59 = 0.93 ng/mL, not 0.80
What none of this tells you is whether 0.8 ng/mL is high or low. Growth hormone is secreted in pulses; a value drawn at random can be near zero in a healthy adult and several µg/L half an hour later in the same person
The two international standards, and the gap between them
| Standard | Material | Assigned potency | 1 ng/mL converts to |
|---|---|---|---|
| WHO IS 98/574 — current | Recombinant somatropin | 3.0 IU per mg (1.95 mg per ampoule) | 3.0 mIU/L |
| WHO IS 80/505 — superseded | Extracted from human pituitary glands | 4.4 IU per ampoule, containing about 1.70 mg | about 2.6 mIU/L |
| Difference | — | About 14% lower on the old standard | 2.6 against 3.0 |
Why a random growth hormone is close to uninterpretable
| Question being asked | What is actually measured | The role of a random GH |
|---|---|---|
| Is there acromegaly? | IGF-1 first; then failure of GH to suppress below 1 µg/L during an oral glucose tolerance test | The Endocrine Society guideline recommends against relying on random GH to make this diagnosis |
| Is there growth hormone deficiency in an adult? | Peak GH during a stimulation test — insulin tolerance, glucagon or macimorelin | A low random value is expected in health and proves nothing |
| Is a child growing poorly because of GH deficiency? | Auxology and growth velocity first, then stimulation testing, with IGF-1 and IGFBP-3 as supporting measures | Not used |
| Is treated acromegaly in remission? | Age-matched IGF-1, with GH as a secondary measure | Interpreted only alongside IGF-1 |
A factor that changed, and a hormone that pulses
Growth hormone is reported two ways. Mass units — nanograms per millilitre, or the identical micrograms per litre — say how much protein is in the sample. International units say how much biological potency it has when measured against a WHO reference preparation. The bridge between them is a potency assignment rather than a molecular weight: the current International Standard for somatropin, 98/574, carries 3.0 International Units per milligram, so one microgram per litre is three milli-international-units per litre, and one mIU/L is one µIU/mL.
The factor has not always been three. Before recombinant somatropin became the reference material, the standard was 80/505, prepared from human pituitary glands and assigned 4.4 International Units per ampoule for an ampoule containing roughly 1.70 milligrams of hormone — about 2.6 units per milligram. A laboratory using the old standard therefore reported about 14% fewer milli-units for the same concentration of hormone, and a mIU/L figure quoted in an older paper back-converts to a mass concentration about 15% higher than the same figure would today. Where an old result is being compared with a new one, or a threshold is carried across from older literature, the mass units are the safer currency because they do not depend on which ampoule the assay was calibrated against.
There is no molar conversion on this page, and that is not an omission. The International Unit measures what the hormone does, not how many molecules are present, and circulating growth hormone is not one molecule: the 22-kilodalton form predominates but a 20-kilodalton variant, oligomers and a large binding-protein-bound fraction all circulate alongside it, and assays see them differently. A single molar mass would misdescribe all of that, so no nmol/L figure is offered.
The larger point is that the number being converted rarely answers the question that prompted the test. Growth hormone is secreted in pulses, predominantly during slow-wave sleep, with long intervals in between during which a healthy adult’s level is close to undetectable. A random measurement therefore has an enormous healthy range and almost no discriminating power. Acromegaly is confirmed by failure of growth hormone to suppress below 1 µg/L during an oral glucose load, after IGF-1 has raised the suspicion; deficiency is established by the peak response to a stimulation test, not by a baseline value. IGF-1, which reflects growth hormone exposure integrated over days and does not pulse, is the better screening measurement in both directions. This page will convert your units accurately. It cannot make a random growth hormone mean more than it does.
Frequently asked questions
How do you convert growth hormone from ng/mL to mIU/L?
Multiply by 3. The WHO International Standard for somatropin, 98/574, is assigned 3.0 International Units per milligram, so 1 ng/mL — which is the same as 1 µg/L — equals 3.0 mIU/L, and mIU/L and µIU/mL are the same number. A growth hormone of 0.8 ng/mL is 2.40 mIU/L.
Why do some sources say 1 ng/mL is 2.6 mIU/L?
Because they predate the current standard. The older International Standard 80/505 was extracted from human pituitary glands and worked out at about 2.59 IU per milligram, against 3.0 IU per milligram for the recombinant material that replaced it. Results in mIU/L from before the changeover are about 14% lower than the same concentration would give today, so old and new figures in international units are not directly comparable.
Why is there no nmol/L conversion for growth hormone?
Because the International Unit is a measure of biological potency against a reference preparation, not an amount of substance, and circulating growth hormone is a mixture of isoforms, oligomers and binding-protein-bound hormone rather than a single species with one molecular weight. Any single molar figure would misdescribe what the assay actually reports.
What is a normal growth hormone level?
There is no useful single answer, which is why this page prints no reference interval. Secretion is pulsatile and mostly nocturnal, so a healthy adult’s level swings from near-undetectable to several µg/L within an hour. Acromegaly is diagnosed by failure to suppress below 1 µg/L during an oral glucose load and deficiency by the peak response to a stimulation test — not by a random level.
Should I use growth hormone or IGF-1 to screen for a growth hormone problem?
IGF-1, in almost every case. It is produced in response to growth hormone and has a long half-life, so it reflects average exposure over days rather than the moment the needle went in. The Endocrine Society acromegaly guideline recommends measuring IGF-1 in suspected cases and recommends against relying on random growth hormone levels to make the diagnosis.
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References
- Katznelson L, Laws ER, Melmed S, et al. Acromegaly: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2014;99(11):3933–3951.
- National Institute for Biological Standards and Control. WHO International Standard: Somatropin, 98/574 — Instructions for Use. Assigned potency 3.0 IU per mg somatropin.
- National Institute for Biological Standards and Control. WHO International Standard: Growth Hormone, Human, Pituitary, 80/505 — Instructions for Use. 4.4 IU per ampoule, approximately 1.70 mg hGH.
- Giustina A, Biermasz N, Casanueva FF, et al. Consensus on criteria for acromegaly diagnosis and remission. Pituitary. 2024. doi:10.1007/s11102-023-01360-1.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.