IGF-1 Blood Test: Reading Your Result by Age

An IGF-1 blood test measures a stable downstream signal of growth hormone activity, not a momentary growth hormone pulse. Read the result against the age-, sex-, and assay-specific interval printed by the testing laboratory. A high or low number can support an endocrine workup, but one result does not diagnose excess or deficiency.

What does an IGF-1 blood test measure?

An IGF-1 blood test measures circulating insulin-like growth factor 1, a hormone produced largely by the liver in response to growth hormone (GH). GH arrives in pulses, so a random GH draw can catch a peak or a trough. IGF-1 changes more slowly and acts as the GH axis’s steadier report card—useful, but not a perfect transcript.

That answers what does IGF-1 measure in practical terms: the integrated effect of GH secretion and GH action. Current acromegaly literature calls IGF-1 the first-line biochemical test because it is relatively stable through the day and usually does not require fasting. Nutrition, liver and kidney function, diabetes, pregnancy, puberty, and oral estrogen can still shift the result (Fleseriu et al., 2026).

What is the IGF-1 normal range by age?

The IGF-1 normal range by age rises toward puberty and then declines through adulthood, but there is no single correct range for every laboratory. The chart below is an example from healthy adults tested with the IDS iSYS assay. It is useful for seeing the age pattern, not for overruling the interval beside your own result.

Age	Male iSYS range (ng/mL)	Female iSYS range (ng/mL)
18–20	168–391	155–421
21–23	147–346	144–383
24–26	132–313	134–353
27–29	122–292	126–330
30–39	108–265	113–294
40–49	91–233	97–253
50–59	81–214	80–209
60–69	75–208	64–170
70–89	64–192	56–154

This IGF-1 levels chart comes from a multicenter reference study of healthy adults. Its ranges cover the central 95% of results, not a boundary between healthy and sick. Children need narrower age bands and often pubertal-stage context because IGF-1 changes sharply around puberty (Bidlingmaier et al., 2014).

Why does the range on your own report win?

Your report’s range wins because IGF-1 intervals are assay-specific as well as age- and sex-specific. In one study, researchers ran samples from the same healthy adult population through six commercial assays. For men aged 30–39, the upper limit ranged from 265 ng/mL with iSYS to 348 ng/mL with IMMULITE 2000. Same people; different measuring systems.

The six-assay comparison found marked differences in upper limits and recommended using the same assay when following a person over time. A standard-deviation score, also called an IGF-1 Z-score or SDS, can help by showing where a result sits relative to matched reference data. Comparing raw numbers from different laboratories is shakier.

How should you read IGF-1 test results?

IGF-1 test results make the most sense in four layers: the value and units, the laboratory’s reference interval, the Z-score if supplied, and the clinical reason for testing. “High,” “normal,” and “low” are flags for interpretation, not diagnoses by themselves. Molecular Reference sells no blood tests, sermorelin, MK-677, or hormone treatment; there is nothing here to upsell after the chart.

• Above range: Persistent elevation can support evaluation for GH excess, including acromegaly in adults. Equivocal results may be repeated and interpreted with symptoms and further GH testing.
• Within range: A normal result usually argues against GH excess, but does not rule out adult GH deficiency.
• Below range: A low value can occur with GH deficiency, but also with malnutrition, liver disease, poorly controlled diabetes, oral estrogen use, and other conditions.

The Endocrine Society’s adult GH-deficiency guideline says a normal IGF-1 does not exclude deficiency; confirmation usually requires a GH stimulation test in the right clinical setting. One biomarker is a clue, not a verdict wearing a lab coat.

Can one abnormal result diagnose a GH disorder?

One abnormal IGF-1 result usually cannot diagnose a GH disorder because biological variation, assay differences, health conditions, and pretest probability all matter. Recent acromegaly guidance uses clearly elevated age-adjusted IGF-1 alongside characteristic clinical signs; borderline or discordant results can lead to repeat IGF-1 testing and, when useful, an oral glucose tolerance test for GH suppression.

Low results need the same restraint. Adult GH deficiency is uncommon without a relevant pituitary or hypothalamic history, and the symptoms overlap with far more common problems. Repeating a surprising result with the same laboratory preserves comparability. Switching assays midstream can turn measurement noise into a medical plot twist.

How do MK-677, sermorelin, and HGH affect IGF-1?

MK-677, sermorelin, and HGH can raise IGF-1 through different points on the GH axis, so an IGF-1 result taken during use is not a clean untreated baseline. MK-677 activates the ghrelin receptor and prompts pulsatile GH release. Sermorelin mimics growth-hormone-releasing hormone. HGH supplies growth hormone directly.

An increased number shows biochemical target engagement—the axis moved. It does not prove added muscle, faster recovery, or any other desired outcome. The distinction matters especially with MK-677: human trials show that the compound can raise IGF-1, while the result still needs separate outcome evidence. The guide to peptides versus HGH explains how those routes differ before the blood reaches the laboratory.

What is the useful takeaway from your result?

The useful takeaway is the result’s position within the matching laboratory interval, plus whether it fits the reason the test was ordered. Keep the assay, units, age band, sex-specific range, and Z-score together when comparing tests over time. A web chart can provide context; it cannot replace that packet of information.

IGF-1 is valuable precisely because it smooths GH’s pulses into a more readable signal. The tradeoff is that the signal also reflects age, sex, assay design, physiology, and health context. Read the printed range first, then decide whether the number is ordinary, worth repeating, or part of a broader endocrine workup.