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Somatomedin C (IGF 1)

Immunology & Autoimmune

IGF-1IGF-IInsulin-like Growth Factor 1Somatomedin C

Review status

Currently under review

Pending specialist review and validation.

What it shows

Somatomedin C, also called insulin-like growth factor 1, is a hormone mostly made by your liver in response to growth hormone from the pituitary gland. It helps regulate normal growth of bones and tissues and supports repair and metabolism throughout life.

Unlike growth hormone, which rises and falls during the day, IGF-1 stays relatively steady, so it is a useful indicator of overall growth hormone activity. The test is done on a blood sample and is interpreted using age- and sex-specific standards because IGF-1 naturally varies across the lifespan.

Why it matters

Your clinician may order IGF-1 to evaluate concerns about growth in children and teens, or to assess for too much or too little growth hormone activity in adults. It also helps monitor treatment for conditions linked to excess growth hormone and to track response to growth hormone therapy when deficiency is suspected.

IGF-1 levels can be influenced by nutrition, liver and kidney function, thyroid status, diabetes control, and certain medicines. Understanding your IGF-1 level in context can help identify underlying endocrine, nutritional, or systemic issues and guide next steps in testing or treatment.

Understanding your results

IGF-1 results are interpreted in relation to your age, sex, and clinical situation. A value above the expected range for your group can suggest increased growth hormone activity, while a value below the expected range can be seen with reduced growth hormone activity, poor nutrition, liver disease, hypothyroidism, or other medical conditions. Medications such as oral estrogens and treatments that affect growth hormone can also shift results.

One result rarely tells the whole story. Your clinician may correlate IGF-1 with symptoms, exam findings, other labs, and imaging. Sometimes repeat testing or specialized stimulation or suppression tests are recommended. If your result is unexpected, do not be alarmed; discuss timing of medicines, supplements, and any recent illness so the result can be interpreted accurately.

Reference ranges

- – - nmol/L
Female
0 days – 18 years
- – - nmol/L
Male
0 days – 18 years
13.3 – 42.6 nmol/L
Female
18 years – 29 years
17.8 – 47.6 nmol/L
Male
18 years – 29 years
13.3 – 42.6 nmol/L
Female
29 years – 40 years
17.8 – 47.6 nmol/L
Male
29 years – 40 years
14 – 42.9 nmol/L
Female
40 years – 50 years
14.7 – 42.4 nmol/L
Male
40 years – 50 years
13 – 40.8 nmol/L
Female
50 years – 60 years
11 – 34.1 nmol/L
Male
50 years – 60 years
11.3 – 25.4 nmol/L
Female
60 years – 70 years
13.1 – 29.1 nmol/L
Male
60 years – 70 years
- – - nmol/L
Female
70 years – 150 years
- – - nmol/L
Male
70 years – 150 years

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

Factors that could impact Somatomedin C (IGF 1)

  • Age and puberty

    IGF-1 changes with growth and development. Levels rise during puberty and gradually decline in adulthood, so results must be matched to age and sex to avoid over- or under-interpretation.

  • Nutrition and overall health

    Poor calorie or protein intake, eating disorders, chronic illness, and frailty can lower IGF-1. Repleting nutrition or recovering from illness may normalize results over time.

  • Liver and kidney function

    The liver produces IGF-1 and the kidneys influence binding proteins. Liver disease or advanced kidney disease can reduce measured IGF-1 or alter its binding, affecting interpretation.

  • Thyroid and diabetes control

    Hypothyroidism and poorly controlled diabetes can lower IGF-1, while hyperthyroidism can raise it. Optimizing thyroid status and glucose control improves the reliability of results.

  • Medications and hormones

    Oral estrogens can lower IGF-1, especially when taken by mouth. Growth hormone therapy increases IGF-1, and drugs used to treat growth hormone excess can decrease it. Androgens, glucocorticoids, and dopamine agonists may also affect levels.

  • Pregnancy and contraceptives

    Pregnancy and some hormonal contraceptives change IGF-binding proteins and can shift IGF-1 results. Tell your clinician about pregnancy or hormone use so the result can be interpreted correctly.

  • Acute illness and stress

    Severe illness, infection, trauma, or major stress can transiently lower IGF-1. When possible, testing is best performed when you are clinically stable and well.

  • Assay and supplements

    Different laboratories and methods use different calibrations and units. High-dose biotin supplements can interfere with some immunoassays. Use the same lab for follow-up and tell staff about supplements.

2026

References

  1. McGill University Health Centre. (2015, September 28). Somatomedin C (IGF 1) (Task CD 699199). Laboratory reference ranges.
  2. McGill University Health Centre. (2015, October 05). Somatomedin C (IGF 1) (Task CD 699199). Laboratory reference ranges.
  3. Melmed, S., Bronstein, M. D., Chanson, P., Klibanski, A., Casanueva, F. F., Wass, J. A. H., Strasburger, C. J., Luger, A., & Clemmons, D. R. (2014). Acromegaly: An Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism, 99(11), 3933–3951.
  4. Molitch, M. E., Clemmons, D. R., Malozowski, S., Merriam, G. R., & Vance, M. L. (2011). Evaluation and treatment of adult growth hormone deficiency: An Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism, 96(6), 1587–1609.
  5. Grimberg, A., DiVall, S. A., Polychronakos, C., Allen, D. B., Cohen, L. E., Quintos, J. B., Rossi, W. C., Feudtner, C., Murad, M. H., & Murad, M. H. (2016). Guidelines for growth hormone and insulin-like growth factor-I treatment in children and adolescents: Growth Hormone Research Society and Pediatric Endocrine Society. Hormone Research in Paediatrics, 86(6), 361–397.