Human Growth Hormone (HGH)

EPIC Test Name: GROWTH HORMONE

Collect specimen in SST tube. Allow to clot. Centrifuge and store refrigerated. Transport to lab. If transportation will be delayed more than 8 hours, aliquot serum and freeze.

Specimen Type: Serum (preferred) or Plasma
Container/Tube: SST or Lithium Heparin (Green top)
Sample Volume: 1 mL
Minimum Volume: 0.2 mL (Repeat testing is not possible with this specimen volume.)
Storage: Refrigerate
Stability (collection to time of analysis/testing):

• Refrigerated: 8 hours
• Frozen: 2 months

The growth hormone (GH) is measured in order to diagnose GH deficiency or GH excess. The GH immunoassay measures all forms of GH [appendix 1].

In general, random measurements of GH may not be informative. To diagnose GH deficiency, usually GH is measured in the basal state and following any of a variety of stimuli. Stimulated GH concentrations of 7 to 10 ng/mL or greater are often interpreted as defining GH sufficiency in children. Stimulated GH concentrations of 3 to 5 ng/mL or greater are often interpreted as defining GH sufficiency in adults. Low IGF-I level s in children are compatible with GH deficiency but medical problems other than GH deficiency will lower IGF-I such as hypothyroidism, chronic disease and malnutrition.

To diagnose GH excess, usually GH is measured in the basal state and following the administration of oral glucose. In general 2 hours after the administration of oral glucose, GH levels should normally be less than 1 to 2 ng/mL. . Elevated IGF-I level s are compatible with GH excess.

Appendix 1

GH has two disulfide bridges (amino acids 54 and 165, and amino acids 182 and 189).59 Structurally, GH has four main alpha-helices, and within the connecting loops three mini-helices.

Two circulating forms of GH are present: a 22 kDa form that is a 191 amino acid chain (full-length GH) representing 85 to 90% of circulating GH, and a 20 kDa GH that lacks amino acids 32 through 46. The 20 kDa form of GH results from alternative splicing of the GH mRNA transcript. In addition to the 22 kDa and 20 kDa forms, circulating GH exists as aggregates and oligomers. “Big GH” is a dimer of GH monomers, and “big-big GH” is GH associated with its binding protein (GHBP). GHBP is the external domain of the GH receptor (GHR), which binds GH with high affinity and is produced by cleavage of the GHR. Approximately 55% of all circulating GH forms are monomeric; big GH and big-big GH represent ≈27% and ≈18% of circulating GH, respectively. Approximately 50% of GH is not bound to GHBP, ≈45% is bound to GHBP, and the remaining 5% of GH is bound to low-affinity binding proteins.

^References

• ^{Winter WE; Rosenbloom AL. Biochemistry of Growth. In: Biochemical Basis of Pediatric Disease, 4th Edition, D Dietzen, MJ Bennett, ECC Wong (eds), AACC Press, Washington, DC, 2010, pp: 171-194.}
• ^{Winter WE, Hardt NS, Harris NS. Disorders of the Anterior and Posterior Pituitary. In: Contemporary Practice in Clinical Chemistry, 2nd Edition. WA Clarke, DR (ed). AACC Press, Washington, DC, 2011; pp: 411-430.}
• ^{Winter WE, Jialal I, Vance ML, Bertholf RL: Pituitary Function and Pathophysiology. : In: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 5th Edition, C Burtis, E Ashwood, D Bruns (eds), Elsevier Saunders, St. Louis, Mo, 2012; pp. 1803-1845.}
• ^{Winter, W.E., Bazydlo, LA, Harris, NS. Quick Guide to Endocrinology. AACC Press, Washington, DC. 2013, 189 pages.}
• ^{Jialal, I, Winter WE, and RL Berthold. “Disorders of the Pituitary.” Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics. Eds, Carl A Burtis and David E. Bruns. Seventh Edition. ElSevier: 2015. 769-784.}

Solid-phase, two-site chemiluminescent immunometric assay

1-3 Business Days

Males: <3 ng/mL
Females: <8 ng/mL