Insulin-Like Growth Factor-I (IGF-I)

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Subject: Insulin-Like Growth Factor-I (IGF-I)

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Definition

  • IGF-I is secreted by hypothalamus; release is mediated by growth hormone (GH) in many tissues, especially hepatocytes. It is a single polypeptide chain with 70-amino-acid residues with a molecular mass of 7,649 Da. It is structurally homologous to IGF-II and insulin. IGF-I circulates primarily in a high molecular weight tertiary complex with IGF-binding protein-3 (IGFBP-3) and acid-labile subunit. Plasma IGF-I levels are barely detectable at birth, rise gradually during childhood, peak during mid-puberty until approximately 40 years of age, and then decline gradually. Maternal plasma levels increase during pregnancy.

  • Normal range: see Table 16.50; 0–7 days: <26 ng/mL; 8–15 days: <41 ng/mL.

 
TABLE 16–50
Normal Range of IGF-I

Use

  • Diagnosis of acromegaly and pituitary deficiency; preferable to GH because it is constant after eating and during the day

  • Help determine optimum dosage of GH

  • Screening other growth disorders

  • Assessing nutritional status

  • Monitoring effectiveness of nutritional repletion; a more sensitive indicator than prealbumin, transferrin index, or retinol-binding protein

Interpretation

Increased In

  • Acromegaly and gigantism

  • Pregnancy (2–3 times nonpregnant values)

Decreased In

  • Pituitary deficiency

  • Laron dwarfism

  • Anorexia or malnutrition

  • Acute illness

  • Hepatic failure

  • Hypothyroidism

  • DM

  • Normal aging

 
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