Insulin-like growth factor I in blood

Serum insulin-like growth factor I

The main factor determining the concentration of IGF-I in the blood serum is age. The concentration of IGF-I in the blood increases from very low values (20-60 ng/ml) at birth and reaches peak values (600-1100 ng/ml) during puberty. Already in the second decade of a person's life, the level of IGF-I begins to decline rapidly, reaching average values (350 ng/ml) at the age of 20, and then decreases more slowly with each decade. At the age of 60, the concentration of IGF-I in the blood is no more than 50% of that at the age of 20. No daily fluctuations in the concentration of IGF-I in the blood have been identified.

Conditions affecting the concentration of STH in the blood

Increased concentration	Decreased concentration
Acromegaly and gigantism Fasting, stress, alcoholism Chronic renal failure Post-traumatic and post-operative conditions Porphyria, hyperglycemia Ectopic production by tumors of the stomach, lungs Hyperpituitarism Physical activity ACTH, vasopressin, estrogens, norepinephrine, dopamine, serotonin, clonidine, propranolol, bromocriptine, arginine, insulin, vitamin PP, amphetamine	Pituitary dwarfism Hypercorticism Obesity Chemotherapy, radiotherapy Surgical interventions Itsenko-Cushing syndrome Factors causing hyperglycemia Hypopituitarism Anencephaly in the fetus Progesterone, glucocorticosteroids, phenothiazines, somatostatin, glucose

Reference values for serum IGF-I concentrations

Age, years	Floor	IGF-I, ng/ml
1-3	Male	31-160
	Female	11-206
3-7	Male	16-288
	Female	70-316
7-11	Male	136-385
	Female	123-396
11-12	Male	136-440
	Female	191-462
13-14	Male	165-616
	Female	286-660
15-18	Male	134-836
	Female	152-660
18-25	Male	202-433
	Female	231-550
26-85	Male	135-449
	Female	135-449

The concentration of IGF-I in the blood depends on the growth hormone, as well as on T ₄. Low levels of IGF-I are detected in patients with severe T ₄ deficiency. Substitution therapy with sodium levothyroxine leads to normalization of the concentration of IGF-I in the blood serum.

Another factor determining the concentration of IGF-I in the blood is nutritional status. Adequate protein and energy supply of the body is the most important condition for maintaining normal concentration of IGF-I in the blood in both children and adults. In children with severe energy and protein deficiency, the concentration of IGF-I in the blood is reduced, but can be easily corrected by normalizing nutrition. Other catabolic disorders, such as liver failure, inflammatory bowel disease or renal failure, are also associated with low levels of IGF-I in the blood.

In clinical practice, the study of IGF-I is important for assessing the somatotropic function of the pituitary gland.

In acromegaly, the concentration of IGF-I in the blood is constantly increased and is therefore considered a more reliable criterion for acromegaly than the level of growth hormone. The average concentration of IGF-I in the blood serum of patients with acromegaly is approximately 7 times higher than the normal age value. The sensitivity and specificity of the IGF-I study for the diagnosis of acromegaly in patients over 20 years of age exceeds 97%. The degree of increase in the concentration of IGF-I in the blood serum correlates with the activity of the disease and the growth of soft tissues. Determination of the content of IGF-I in the blood serum is used to monitor the effectiveness of treatment, since it correlates well with the residual secretion of growth hormone.

The following laboratory parameters are considered to be the criteria for curing acromegaly:

• fasting blood growth hormone concentration below 5 ng/ml;
• the concentration of growth hormone in the blood is below 2 ng/ml during OGTT;
• the concentration of IGF-I in the blood is within normal values.

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