Growth Hormone Replacement in Older Men Workup

Updated: Dec 14, 2015
  • Author: Angela Gentili, MD; Chief Editor: George T Griffing, MD  more...
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Workup

Laboratory Studies

A single measurement of plasma GH levels is difficult to interpret because of the pulsatile secretion of GH. levels of IGF-1 vary little during the day; therefore, assays of IGF-1 have been used as a better indicator of the status of the GH–IGF-1 axis. Plasma IGF-1 levels decrease with aging, and an inverse correlation exists between age and IGF-1 levels. A cutoff IGF-1 level cannot be used for diagnostic purposes because the GH–IGF-1 axis is influenced by other factors besides aging (see Pathophysiology). Furthermore, evidence of an association between IGF-1 levels and measures of muscle strength, body composition, and physical functioning in older adults is lacking.

A single measurement of plasma GH levels is difficult to interpret because of the pulsatile secretion of GH. levels of IGF-1 vary little during the day; therefore, assays of IGF-1 have been used as a better indicator of the status of the GH–IGF-1 axis. Plasma IGF-1 levels decrease with aging, and an inverse correlation exists between age and IGF-1 levels. A cutoff IGF-1 level cannot be used for diagnostic purposes because the GH–IGF-1 axis is influenced by other factors besides aging (see Pathophysiology). Furthermore, evidence of an association between IGF-1 levels and measures of muscle strength, body composition, and physical functioning in older adults is lacking.

According to 2007 consensus guidelines for the diagnosis and treatment of adults with GH deficiency, [14] the following patients should be considered for testing for growth hormone deficiency (GHD):

  • Patients with signs and symptoms of hypothalamic-pituitary disease
  • Those who have received cranial irradiation or tumor treatment
  • Those with traumatic brain injury or subarachnoid hemorrhage

In these patients, a low IGF-1 concentration increases the likelihood of GHD. Further testing may include a stimulation test, such as the insulin tolerance test (ITT), GHRH + arginine testing, GHRH + GHRP testing, or a glucagon stimulation test. The ITT is contraindicated in patients with ischemic heart disease or seizure disorders, and many authorities prefer not to use the ITT in patients older than 60 years. [15] Patients who are deficient in at least 3 pituitary hormones and have an IGF-I level below the reference range have a greater than 97% chance of being GH deficient. For more details on how to diagnose GHD, see Hypopituitarism (Panhypopituitarism).