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.
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TABLE 16 " “50Normal Range of IGF-IView LargeTABLE 16 " “50Normal Range of IGF-I Age (y) Central 95% Range 16 d to 1 y 55 " “327 2 51 " “303 3 49 " “289 4 49 " “283 5 50 " “286 6 52 " “297 7 57 " “316 8 64 " “345 9 74 " “388 10 88 " “452 11 111 " “551 12 143 " “693 13 183 " “850 14 220 " “972 15 237 " “996 16 226 " “903 17 193 " “731 18 163 " “584 19 141 " “483 20 127 " “424 21 " “25 116 " “358 26 " “30 117 " “329 31 " “35 115 " “307 36 " “40 109 " “284 41 " “45 101 " “267 46 " “50 94 " “252 51 " “55 87 " “238 56 " “60 81 " “225 61 " “65 75 " “212 66 " “70 69 " “200 71 " “75 64 " “188 76 " “80 59 " “177 81 " “85 55 " “166
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