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Insulin-Like Growth Factor–Binding Protein-3 (IGFBP-3)


Definition


  • This 264-amino-acid peptide (molecular weight, 29 kDa) is produced by the liver. It is the most abundant of a group of IGFBPs that transport and control bioavailability and half-life of insulin-like growth factors (IGFs), in particular IGF-I. In addition to its IGF-binding function, IGFBP-3 also exhibits intrinsic growth-regulating effects that are not yet fully understood but have evoked interest with regard to a possible role of IGFBP-3 as a prognostic tumor marker. Other name: somatomedin C " �binding protein.
  • Normal range: see Table 16.49.

� �
TABLE 16 " �49Normal Ranges for IGFBP-3View LargeTABLE 16 " �49Normal Ranges for IGFBP-3 Age (in years Unless Otherwise Specified) Reference Range (mg/mL) 0 " �15 d 0.5 " �1.4 1 0.7 " �3.6 2 0.8 " �3.9 3 0.9 " �4.3 4 1.0 " �4.7 5 1.1 " �5.2 6 1.3 " �5.6 7 1.4 " �6.1 8 1.6 " �6.5 9 1.8 " �7.1 10 2.1 " �7.7 11 2.4 " �8.4 12 2.7 " �8.9 13 3.1 " �9.5 14 3.3 " �10 15 3.5 " �10 16 3.4 " �9.5 17 3.2 " �8.7 18 3.1 " �7.9 19 2.9 " �7.3 20 2.9 " �7.2 21 " �25 3.4 " �7.8 26 " �30 3.5 " �7.6 31 " �35 3.5 " �7.0 36 " �40 3.4 " �6.7 41 " �45 3.3 " �6.6 46 " �50 3.3 " �6.7 51 " �55 3.4 " �6.8 56 " �60 3.4 " �6.9 61 " �65 3.2 " �6.6 66 " �70 3.0 " �6.2 71 " �75 2.8 " �5.7 76 " �80 2.5 " �5.1 81 " �85 2.2 " �4.5

Use


  • Diagnosing growth disorders
  • Diagnosing adult growth hormone deficiency
  • Monitoring of recombinant human growth hormone treatment
  • Possible adjunct to IGF-I and growth hormone in the diagnosis and follow-up of acromegaly and gigantism

Interpretation


Increased In


  • Overproduction of GH
  • Excessive rhGH therapy
  • Chronic renal failure

Decreased In


  • GH deficiency
  • GH resistance
  • Fasting/chronic malnutrition
  • Hepatic failure
  • Diabetes mellitus

Limitations


  • IGF-I and IGFBP-3 reference ranges are highly age dependent, and results must always be interpreted within the context of the patients age.
  • Discrepant IGFBP-3 and IGF-I results can sometimes occur due to liver and kidney diseases; however, this is uncommon, and such results should alert laboratories and physicians to the possible occurrence of a preanalytic or analytic error.
  • At this time, IGFBP-3 cannot be reliably used as a prognostic marker in breast, colon, prostate, or lung cancer.
  • IGFBP-3 assays exhibit significant variability among platforms and manufacturers. Direct comparison of results obtained by different assays is problematic. Rebaselining of patients is preferred if assays are changed.
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