What is the role of GH 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

Many RIAs are available to measure GH levels, and all offer limited accuracy. Repeated measurements may vary by as much as 3-fold, even when the tests are conducted in laboratories with personnel experienced in the procedures. This variation is observed because several molecular forms of GH are identified in the serum and because polyclonal (instead of monoclonal) antibodies are used. To improve standardization, use of a 22-kDa recombinant human growth hormone (rhGH) reference preparation with an assigned potency of 3 IU/mg has been recommended. When assay data are reported, a clear statement of the method should be included. The optimal assay measures the 22-kDa hGH species by using a monoclonal antibody. [14, 15, 21, 55, 23, 56]

Serum GH concentrations remain constitutively elevated from the newborn period to as late as 6 months of age. Therefore, a serum GH level of less than 20 ng/mL in infants younger than 6 months suggests GHD. However, a random hGH level is not diagnostic in patients older than 6 months because hGH is intermittently secreted in brief nocturnal pulses (of 10-15 minutes during deep sleep) beyond early infancy. GHD cannot be diagnosed on the basis of a single random serum GH concentration at any age.


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