Insulin-like-growth-factor-I (IGF1; IGF-I; also called somatomedin C (SM-C)) is a laboratory parameter that shows high similarity to insulin. It is one of the differentiation and growth factors. The majority of IGF-1 is synthesized in the liver. IGF-1 is bound to special binding proteins (insulin-like-growth-factor-binding-protein – IGFBP) that circulate in the blood. In this process, the action of IGF-1 is regulated by these proteins. In this context, the STH secretion status generally correlates well with the serum concentration of IGF-1 = somatomedin C, a growth-promoting peptide hormone that is produced in the liver but also in other organs under the influence of STH. After STH release, an IGF-1 increase is not to be expected until 5 to 6 hours later. IGF-1 reaches the target organs via the bloodstream, where it is bound to the transport protein “insulin-like-growth-factor-binding-protein-3″. IGF-1 exerts its effect via membrane-bound IGF receptors, which are detectable in almost all tissues and on most cell types. Since the STH secretion status is difficult to determine directly, it is usually determined with very good correlation via the IGF-1 concentration in serum. Accordingly, serum IGF-1 concentration decreases with increasing age in analogy to STH secretion status. However, STH does not come into action exclusively through IGFs, and IGFs also have STH-independent effects. Serum levels of IGF-1 physiologically decline gradually after puberty. IGF-1 is stimulated primarily by other hormones (thyroid hormones; adrenal and ovarian steroids), but also by food intake (dinner cancelling; fasting), weight reduction, exercise, sleep quality and duration, and stress reduction. It is inhibited by GHRH (growth hormone releasing hormone) and somatostatin (growth hormone releasing inhibitory hormone = GHIH). IGF-II (somatomedin A; SM-A) is distinguished from IGF-1. However, the significance of this parameter has not yet been conclusively clarified.
Procedure
Material needed
- Blood serum
Preparation of the patient
- Not necessary
Disruptive factors
- Not known
Standard values
| Age | Normal values |
| 2nd month of life (LM)-5th year of life (LY). | 20-250 ng/ml |
| 6-9LJ | 100-476 ng/ml |
| 9-11 LJ | 110-600 ng/ml |
| 11-16 LJ | 250-1,100 ng/ml |
| 17-55 LY | 125-460 ng/ml |
| > 55. LJ | 70-290 ng/ml |
The yellow highlighted range is the therapeutic target of STH substitution therapy in somatopause; mean IGF-1 concentrations of 200 ng/ml are targeted. Women usually have higher levels!
Indications
- Suspected growth disorders
- Suspicion of endocrine tumors
- Somatopause – progressive reduction in STH secretion over the adult life span. This culminates in a nadir and consistently lowered serum STH levels (IGF-1 ↓; IGFBP-3 ↓) from around age 50.
Interpretation
Interpretation of increased values
- Obesity (obesity)
- Acromegaly – endocrinological disorder caused by overproduction of the growth hormone somatotropin (STH), with marked enlargement of the body end limbs or protruding parts of the body (acras), such as the hands, feet, lower jaw, chin, nose, and eyebrow ridges.
- Gravidity (pregnancy)
Interpretation of lowered values
- Malignant tumor diseases
- Chronic hepatitis (inflammation of the liver)
- Diabetes mellitus – in poor metabolic status.
- Nutritional disorders such as malabsorption – disturbance of food splitting and absorption in the intestine.
- Hypothyroidism (underactive thyroid gland)
- Cachexia (emaciation)
- Laron syndrome – genetically caused short stature.
- Short stature
- Somatopause
- Sepsis (blood poisoning)
- Trauma (injuries)
- Malnutrition
Other notes
- IGF-1 is used therapeutically in studies
