IGF-1 (Somatomedin C) Test: Normal Ranges & Meaning

Understanding the IGF-1 (Somatomedin C) Blood Test

A 45-year-old man came to my clinic concerned about persistent fatigue and muscle weakness. His blood work revealed a low IGF-1 level, prompting further investigation into his pituitary function. This scenario is common in my practice—IGF-1, also known as Somatomedin C, is a key marker for growth hormone (GH) activity and tissue growth.

Insulin-like Growth Factor 1 is produced primarily in the liver in response to growth hormone stimulation. It mediates many of GH's effects, including cell growth, protein synthesis, and bone density regulation. The test is considered a reliable reflection of average GH secretion over time, unlike GH itself which is released in pulses.

Why Is the IGF-1 Test Ordered?

My patients typically ask me why they need this test. The most common reasons include:

• Suspected growth hormone deficiency in children (short stature, delayed puberty) or adults (fatigue, reduced muscle mass, osteoporosis).
• Evaluation of acromegaly (excess GH in adults) or gigantism (excess GH in children), often accompanied by symptoms like enlarged hands/feet, coarse facial features, or headaches.
• Monitoring of known GH disorders during treatment (e.g., GH replacement therapy or suppression after pituitary surgery).
• Investigation of pituitary tumours or other conditions affecting GH secretion.

How to Prepare for the IGF-1 Test

Fasting is not required, though some labs prefer a morning sample as GH secretion has a diurnal pattern. Avoid vigorous exercise and high-protein meals 12 hours before the test, as these can transiently affect levels. Inform your doctor about any medications—especially oestrogen, glucocorticoids, or insulin—as they may interfere.

Reference Ranges by Age and Gender

IGF-1 levels peak during puberty and decline steadily with age. Reference intervals vary by laboratory and assay method. The table below gives typical ranges in ng/mL for healthy individuals. Always interpret results alongside your specific lab's norms.

Note: Ranges shown are approximate. The LOINC code for this test is 30522-7 (IGF-1, serum).

What Does a Low IGF-1 Level Mean?

Low IGF-1 suggests insufficient growth hormone action. In children, this can indicate GH deficiency leading to slow growth. In adults, causes include pituitary damage (e.g., tumour, surgery, radiation), hypopituitarism, malnutrition, liver disease, or uncontrolled diabetes. My patients with low levels often report decreased energy, reduced muscle strength, and trouble losing weight.

Can Stress or Diet Lower IGF-1?

Yes. Chronic stress, calorie restriction, and sleep deprivation can suppress GH and thus lower IGF-1. In my experience, correcting these factors often improves levels without medication. However, consistently low levels warrant endocrine evaluation.

What Does a High IGF-1 Level Mean?

Elevated IGF-1 points to excessive GH production. The most common cause is a benign pituitary adenoma causing acromegaly (in adults) or gigantism (in children). Other possibilities include pregnancy, puberty, or rare genetic conditions (e.g., Sotos syndrome). High levels can also occur in some cancers that produce GH or IGF-1.

Is High IGF-1 Dangerous?

Yes, untreated high IGF-1 can lead to serious complications: joint pain, carpal tunnel syndrome, sleep apnoea, diabetes, hypertension, and increased cardiovascular mortality. In acromegaly, early detection via IGF-1 and GH suppression tests is critical to prevent long-term damage.

IGF-1 During Pregnancy

IGF-1 levels naturally rise during pregnancy due to placental production of human placental lactogen and changes in binding proteins. This increase supports foetal growth. My pregnant patients often have levels 2-3 times higher than non-pregnant values. No special action is needed unless there is suspicion of pituitary disease.

Interpreting Your Results

IGF-1 should be interpreted in the context of age, sex, and clinical symptoms. A single abnormal level is rarely diagnostic; dynamic testing (e.g., GH stimulation or suppression tests) is often needed. If you have concerns about your result, consult an endocrinologist. In my practice, I always consider the whole picture—not just the number.

How to Naturally Optimise IGF-1 Levels

For those with borderline low levels, lifestyle changes can help:

• Quality sleep (7-9 hours) – GH is mainly released during deep sleep.
• Regular exercise, especially high-intensity interval training.
• Adequate protein intake (0.8-1.2 g/kg body weight).
• Stress management through meditation or therapy.
• Avoid smoking and limit alcohol.

These steps are safe and beneficial for overall health. However, if you have a diagnosed GH disorder, specific medical treatment is essential.