Overview
Insulin like Growth Factor 1 (IGF-1), also known as Somatomedin C, is a peptide hormone that plays a central role in growth, development, and tissue maintenance. It is a 70–amino-acid polypeptide with three disulfide bonds and shares structural similarity with insulin. The IGF-1 gene is located on chromosome 12.
Insulin like Growth Factor 1 is produced primarily by the liver in response to stimulation by growth hormone (GH). It mediates most of the biological effects of GH and also regulates GH secretion through negative feedback on the pituitary gland. Because IGF-1 levels remain relatively stable throughout the day compared to the pulsatile secretion of GH, IGF-1 measurement is considered a reliable indicator of overall GH activity. Insulin-like Growth Factor 1
Structure and Molecular Characteristics
Insulin like Growth Factor 1 is a single-chain polypeptide stabilized by three disulfide bridges. Its molecular structure allows it to bind efficiently to the IGF-1 receptor, a transmembrane receptor tyrosine kinase widely expressed in many tissues.
The widespread distribution of IGF-1 receptors enables the hormone to exert coordinated growth-promoting effects across multiple organs, including bone, muscle, liver, and connective tissue.
Physiological Functions
Insulin like Growth Factor 1 plays a crucial role in normal childhood growth and adolescent development. Along with GH, it stimulates longitudinal bone growth, skeletal maturation, muscle development, and organ growth.
At the cellular level, Insulin like Growth Factor 1 activates intracellular signaling pathways such as PI3K/Akt and MAPK. These pathways promote cell proliferation, differentiation, survival, and metabolic regulation while inhibiting apoptosis. IGF-1 also supports tissue repair, protein synthesis, and maintenance of lean body mass in adults.
Pathophysiology
IGF-1 acts through endocrine, paracrine, and autocrine mechanisms. Circulating IGF-1 produced by the liver ensures proportional growth and metabolic balance throughout the body.
Locally produced IGF-1 may act independently of systemic GH and contribute to tissue-specific growth. Dysregulation of IGF-1 signaling is associated with growth disorders, metabolic abnormalities, and increased risk of certain malignancies.
Clinical Significance
Insulin like Growth Factor 1 is a key biochemical marker for assessing growth hormone activity. Due to its stable circulating levels, it provides a more consistent assessment than random GH measurements.
Measurement of Insulin like Growth Factor 1 is essential in the diagnosis and management of growth hormone deficiency, acromegaly, and gigantism. It also plays an important role in monitoring treatment response in patients receiving GH-modulating therapies.
Indications for Testing
IGF-1 testing is indicated in children with short stature, delayed growth, or suspected growth hormone deficiency. It is also used in individuals with excessive growth or features suggestive of gigantism or acromegaly.
The test is useful in evaluating pituitary disorders and is often performed alongside other pituitary hormone assessments. IGF-1 levels also reflect nutritional status and are reduced in malnutrition and chronic illness.
Sample Collection and Testing
Patients are advised to observe overnight fasting before sample collection. Approximately 3.0 mL of blood is collected in a plain red-capped tube, and serum is separated for analysis.
Proper pre-analytical handling is important, as factors such as acute illness, liver dysfunction, and poor nutritional status can influence IGF-1 levels. Results should always be interpreted in correlation with clinical findings.
Reference Ranges
IGF-1 levels vary significantly with age and sex. Concentrations are highest during childhood and adolescence, peak during puberty, and gradually decline with advancing age.
Age- and sex-specific reference ranges are essential for accurate interpretation. Z-scores are often used in pediatric populations to assess deviations from normal growth patterns.
Causes and Implications of Low IGF-1
Low IGF-1 levels may result from growth hormone deficiency due to pituitary or hypothalamic disorders. Malnutrition, starvation, chronic liver disease, cirrhosis, and liver failure are common causes.
Endocrine conditions such as hypopituitarism, hypothyroidism, and adrenal insufficiency can also lower IGF-1 levels. Genetic disorders like Laron syndrome, prolonged corticosteroid therapy, and aging contribute to reduced levels.
Clinically, low IGF-1 is associated with impaired growth, reduced bone density, decreased muscle mass, fatigue, and metabolic disturbances.
Causes and Implications of High IGF-1
Elevated IGF-1 levels are most commonly seen in acromegaly and gigantism due to excessive GH secretion, usually from pituitary adenomas. Exogenous GH administration also increases IGF-1 concentrations.
Additional causes include insulin resistance, obesity, chronic kidney disease, and rare genetic conditions. High IGF-1 levels are associated with abnormal skeletal growth, joint problems, insulin resistance, cardiovascular complications, and increased morbidity if untreated.
Limitations
IGF-1 levels are influenced by age, nutritional status, liver function, and systemic illness. Reference ranges vary between laboratories, and results must be interpreted in the appropriate clinical context.
IGF-1 testing should not be used as a standalone diagnostic tool and must always be correlated with clinical findings and other hormonal investigations.
