Growth hormone (GH) is secreted from the pituitary gland. Measurement of GH is primarily of interest in the diagnosis and treatment of various forms of inappropriate growth hormone secretion.
Too much growth hormone (hypersecretion) can cause abnormal growth patterns called acromegaly in adults and gigantism in children. Too little growth hormone (hyposecretion) can cause a slow or flat rate of growth in children, and changes in muscle mass, cholesterol levels, and bone strength in adults.2 Clinical disorders of hyposecretion include dwarfism and unattained growth potential.3
In the diagnosis of growth disorders, measurements of IGF-I are a useful indicator of growth hormone secretion. A normal plasma or serum IGF-I concentration is strong evidence against GH deficiency. A low IGF-I value implies GH deficiency and requires additional testing to determine whether GH secretion is subnormal. Measurement of IGF-I is also useful in assessing change of nutritional status.3
An IGF-I test is often ordered along with GH. IGF-I mirrors GH excesses and deficiencies, but its level is stable throughout the day, making it a useful indicator of average GH levels.1
IGFBP-3 is used as an aid in the evaluation of growth disorders. It is growth hormone (GH) dependent and therefore useful in the evaluation of GH secretion. IGFBP-3 is the main carrier of IGF-I in the body. Blood levels of both these proteins are controlled by GH. IGFBP-3 also helps extend the life of GH in the blood and helps control its effects on body tissues.
Levels of IGFBP-3 are highest during childhood and puberty, and then decrease during adulthood. Levels may also be affected by sexual maturation and nutritional status.4
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