What is the role of IGF RIAs in the workup of hyposomatotropism (growth hormone deficiency [GHD])?

Updated: Jan 24, 2019
  • Author: Sunil Kumar Sinha, MD; Chief Editor: Robert P Hoffman, MD  more...
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Answer

Specific RIAs distinguish IGF-1 and IGF-2. Serum IGF-1 concentrations depend on GH and vary with the patient's age, nutritional status, and sexual maturation. In children younger than 8 years, serum IGF-1 levels may be indistinguishable from levels measured in children with GHD. Concentrations of serum IGF-2 vary less than IGF-1 levels do at a given age; however, serum IGF-2 is less GH dependent than IGF-1.

Rosenfeld and colleagues evaluated the effectiveness of using IGF-1 and IGF-2 RIAs to identify children with GHD. [57] When performed alone, assays for both produced false-positive and false-negative results. However, combined assays helped to correctly identify 96% of children with GHD. Only 0.5% of healthy children had serum concentrations of both IGF-1 and IGF-2 that were below the reference ranges for their age and sex.

Total serum IGF-1 levels represent the combined quantity of unbound IGF-1 (free IGF-1) plus IGF-1 bound to IGFBP-3. Free IGF-1 is postulated to be the bioactive fraction, but it accounts for only a small fraction of the total amount.

Hasegawa and colleagues developed an immunoradiometric assay for free IGF-1 in plasma and reported the relationship of free IGF-1 to GH-secretory status. [58] Low serum levels of free IGF-1 assayed by using this method were highly correlated with complete GHD but not partial GHD. Despite their reduced diagnostic usefulness in patients with partial GHD, free IGF-1 levels may prove useful for assessing compliance with, or the effectiveness of, rhGH therapy.


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