IGF-1 Unit Converter
IGF-1 Unit Converter
Convert IGF-1 (somatomedin C) between ng/mL, µg/L and nmol/L, and read it against an age- and sex-matched adult interval — because an IGF-1 without an age to compare it with is not a result at all.
IGF-1 converter
Mass ⇄ molarIGF-1 180 ng/mL in a man aged 18
The three units
nmol/L = ng/mL × 0.130736
derived from a molecular weight of 7,649 Da for the mature 70-residue peptide
- ng/mL = µg/L
- a nanogram per millilitre and a microgram per litre are the same concentration. One or the other is what your report will show; the number does not change between them
- × 0.130736
- the molar factor, from a mature peptide mass of 7,649 daltons. IGF-1 is 70 amino acids and is one well-defined species, so unlike growth hormone it has a proper molar conversion — but almost no laboratory issues it, and every published reference interval is in mass units
- the age band is part of the result
- IGF-1 peaks in adolescence and falls steadily thereafter. The upper limit for a man of 18 is 506 ng/mL and for a man of 88 it is 176 ng/mL. The same number is unremarkable at one age and clearly abnormal at another, which is why this page will not print a single adult range
- standard deviation score
- the better way to express an IGF-1, and the way paediatric and pituitary services use it: how many standard deviations the result sits from the mean for that age and sex on that assay. It makes results comparable across ages and, when the assay is standardised, across laboratories
- WHO standard 02/254
- the international reference preparation that modern IGF-1 assays are calibrated to. Calibration to it narrowed but did not abolish the differences between methods, so intervals remain assay-specific
Worked example
IGF-1 180 ng/mL in a man aged 18
180 ng/mL = 180 µg/L — the same number in the other mass convention
180 × 0.130736 = 23.53 nmol/L, the molar equivalent, which no report will print
Against the quoted interval for men aged 18, 145–506 ng/mL (18.96–66.15 nmol/L), 180 ng/mL sits within it and near the lower end
The same 180 ng/mL in a man of 70 would sit comfortably in the upper half of that age's 59–230 ng/mL band, and in a man of 88 it would be above the 33–176 ng/mL band altogether
One number, three different readings, decided entirely by the age it is compared against
Adult IGF-1 reference intervals by age and sex (ng/mL)
| Age | Men | Women |
|---|---|---|
| 18 | 145–506 | 117–430 |
| 19 | 122–435 | 113–408 |
| 20 | 116–410 | 108–384 |
| 21–25 years | 109–353 | 101–347 |
| 26–30 years | 101–307 | 91–308 |
| 31–35 years | 95–290 | 84–281 |
| 36–40 years | 90–278 | 79–259 |
| 41–45 years | 84–270 | 74–239 |
| 46–50 years | 81–263 | 70–225 |
| 51–55 years | 74–255 | 65–216 |
| 56–60 years | 68–247 | 60–207 |
| 61–65 years | 64–240 | 57–202 |
| 66–70 years | 59–230 | 52–196 |
| 71–75 years | 53–222 | 48–191 |
| 76–80 years | 45–207 | 42–185 |
| 81–85 years | 40–194 | 39–177 |
| 86–90 years | 33–176 | 34–169 |
What moves IGF-1, and in which direction
| Direction | Cause | Mechanism |
|---|---|---|
| Raised | Acromegaly or gigantism | Sustained growth hormone excess — the main reason to measure it |
| Raised | Adolescence, pregnancy | Physiological; the adolescent peak is roughly double the mid-adult level |
| Raised | Growth hormone treatment, whether prescribed or not | Direct effect; IGF-1 is how replacement is titrated and how misuse is detected |
| Lowered | Growth hormone deficiency | The intended finding — but far from the commonest cause of a low value |
| Lowered | Malnutrition, anorexia nervosa, low energy availability | IGF-1 production is nutrition-dependent; it falls within days of a low protein or energy intake despite normal or high growth hormone |
| Lowered | Liver disease | The liver is the main source of circulating IGF-1 |
| Lowered | Poorly controlled diabetes | Portal insulin is required for hepatic growth hormone sensitivity |
| Lowered | Hypothyroidism, systemic illness, renal failure, oestrogen taken by mouth | Acquired growth hormone resistance by several routes; oral but not transdermal oestrogen lowers IGF-1 by a first-pass hepatic effect |
A number that is meaningless without an age beside it
IGF-1, once called somatomedin C, is made mostly by the liver in response to growth hormone, and it is the measurement that makes the growth hormone axis testable. Growth hormone itself is released in pulses and spends most of the day near zero, so a single blood level says almost nothing. IGF-1 circulates bound to binding proteins with a half-life of hours rather than minutes, so it averages growth hormone exposure over days. That is why it, and not growth hormone, is the first test in suspected acromegaly and the measurement by which replacement is titrated.
The reason this page insists on an age band is that IGF-1 changes more across a normal life than most laboratory results change in disease. It rises through childhood, peaks in mid-adolescence at roughly twice the adult level, and declines steadily from the twenties onward. In the table above, the upper limit for a man of eighteen is 506 ng/mL and for a man of eighty-eight it is 176. A result of 180 ng/mL is near the bottom of the range at eighteen, comfortably mid-range at seventy, and frankly raised at eighty-eight. Reported without an age to compare it against, it is not a result; it is a number. Better still than an age-matched range is a standard deviation score, which states how far the value sits from the mean for that age and sex on that assay and is what pituitary and paediatric services use.
Interpretation is also asymmetric, and this is the part most often got wrong. Almost nothing raises IGF-1 except growth hormone excess, so a clearly raised age-matched value is a strong pointer to acromegaly and is followed by an oral glucose tolerance test with growth hormone sampling. A great many things lower it: malnutrition and low energy availability, anorexia nervosa, liver disease, poorly controlled diabetes, hypothyroidism, renal failure, any severe systemic illness, and oestrogen taken by mouth. In all of those, growth hormone secretion is intact or even increased and the liver is simply not responding to it. A low IGF-1 therefore is not growth hormone deficiency; deficiency is established by the peak response to a stimulation test, and a normal IGF-1 does not exclude it in an adult.
The units are the easy part. Nanograms per millilitre and micrograms per litre are the same number, and one or the other is what every report and every published interval uses. A molar conversion exists — IGF-1 is a single 70-residue peptide of 7,649 daltons, so multiplying by 0.130736 gives nmol/L — but it belongs to conversion tables rather than to laboratory practice, and no reference interval in this page’s sources is published in it.
Frequently asked questions
What is a normal IGF-1 level?
There is no single adult figure: the interval depends on age and sex. On the assay tabulated here it runs from 145–506 ng/mL for a man of eighteen down to 33–176 ng/mL for a man of eighty-eight. Pick the age band above, and use the interval printed on your own report in preference, because it differs between assays.
How do I convert IGF-1 from ng/mL to nmol/L?
Multiply by 0.130736, from a molecular weight of 7,649 daltons for the mature 70-residue peptide. An IGF-1 of 180 ng/mL is 23.53 nmol/L. Nanograms per millilitre and micrograms per litre are the same number, and mass units are what reports and published intervals actually use.
Does a low IGF-1 mean growth hormone deficiency?
No, and this is the commonest misreading. Malnutrition, low energy availability, anorexia nervosa, liver disease, poorly controlled diabetes, hypothyroidism, renal failure, systemic illness and oral oestrogen all lower IGF-1 with growth hormone secretion intact. Deficiency is established by the peak growth hormone response to a stimulation test, not by a low IGF-1.
Why is IGF-1 measured instead of growth hormone?
Because growth hormone is secreted in pulses and is close to undetectable between them, so a random level has almost no discriminating power. IGF-1 has a much longer half-life and reflects growth hormone exposure integrated over days, which makes it the practical screening measurement for both excess and deficiency.
What is an IGF-1 standard deviation score?
How many standard deviations a result sits above or below the mean for that person’s age and sex on that assay. It is the better way to express an IGF-1 because it removes the age effect, making results comparable over time and between patients — which a raw ng/mL figure cannot do.
Related calculators
References
- Bidlingmaier M, Friedrich N, Emeny RT, et al. Reference intervals for insulin-like growth factor-1 (IGF-I) from birth to senescence: results from a multicenter study using a new automated chemiluminescence IGF-I immunoassay conforming to recent international recommendations. J Clin Endocrinol Metab. 2014;99(5):1712–1721.
- Labcorp. Test 010363: Insulin-like Growth Factor 1 (IGF-1) — age- and sex-specific reference intervals, calibrated to WHO recombinant reference standard 02/254. Accessed 2026.
- Katznelson L, Laws ER, Melmed S, et al. Acromegaly: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2014;99(11):3933–3951.
- Molitch ME, Clemmons DR, Malozowski S, et al. Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96(6):1587–1609.
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.