Testing For Adult Growth Hormone Deficiency (AGHD)
Those who show evidence of disease affecting the hypothalamic-pituitary region of the brain and in whom there is intention to treat with growth hormone are usually tested for adult growth hormone deficiency (AGHD).
Advancing age is associated with a marked decrease in growth hormone (GH) or somatotrophin concentrations and secretions, but no study has yet proved that GH therapy is beneficial and safe for otherwise healthy elderly patients. The normal biological decrease in GH secretion that arises with aging (the so-called ‘somatopause’) is not clinically recognized for GH treatment.
Adult Growth Hormone Deficiency
Adult growth hormone deficiency (AGHD) can arise from numerous causes such as genetic defects, congenital malformations, brain injury, subarachnoid hemorrhage, Cushing’s disease, inflammatory and vascular diseases and others. AGHD can also arise because of acromegaly and after neurosurgery and radiotherapy.
Adults with growth hormone deficiency tend to have an increase in fat mass and a relative decrease in muscle mass and, in many instances, decreased quality of life. They may also experience lethargy, disturbed sleep, memory loss, mood changes, brittle skin, nails and hair. Although most of these symptoms can arise with many conditions, in the appropriate clinical setting, they may point to growth hormone deficiency.
Adults with GHD can be grouped into three categories:
- Those with prior childhood growth hormone deficiency (GHD)
- Those who acquire GHD secondary to structural lesions or trauma
- Those with idiopathic (unknown causes) GHD
Childhood GHD is generally further divided into those with organic causes and those with idiopathic (unknown) causes.
Appropriate testing for growth hormone deficiency allows doctors to distinguish between those who have a true and severe GH deficiency and those with confounding factors that are able to lower GH concentrations, such as aging or obesity.
Testing For Gh Deficiency
It is frequently a combination of tests used to detect whether there is an adult growth hormone deficiency (Yuen et al., 2009).
- The insulin tolerance test (during which insulin is injected into a vein).
- A combined GHRH (growth hormone-releasing hormone) + arginine test (administration of arginine for 30 minutes and GHRH for one minute, followed by five blood draws).
- Glucagon test (the simplest of the three, consisting only of collecting blood). This test is common for individuals where the insulin tolerance test is unsuitable).
The insulin tolerance test is still the ‘gold standard’ or reference test, although it may carry an increased risk in those with seizure disorders or cardiovascular disease. It also requires constant monitoring even in healthy adults, although it is quite safe in experienced hands
For the insulin and glucagon tests, the threshold value deﬁning severe GH deﬁciency is 3 micrograms per liter (μg/L), whereas a partial deﬁciency is between 3.01 and 5 micrograms per liter.
For the GHRH + arginine test, the GH threshold depends on body mass index (BMI). The threshold is less than 11 micrograms per liter in those with a normal BMI (< 25), less than 8 micrograms per liter in those that are overweight (BMI 25 to 30) or less than 4 micrograms per liter in those that are obese (BMI > 30).
There are other types of tests, including the growth hormone stimulation test (GHST) which measures the ability of the pituitary to produce growth hormone. This test has now fallen into disuse due to questions about its validity. Doctors may also request blood counts and other hormone tests, such as for testosterone or estrogen.
If testing confirms that there is a growth hormone deficiency, then growth hormone may be prescribed. There are a number of guidelines for treatment, and doctors will use their clinical judgment to assess the risks and benefits of GH treatment and decide on the best treatment regime. Recombinant human growth hormone (rhGH) is the key GH treatment and many adults take rhGH once a day via subcutaneous injection.
- Alexopoulou O, Abs R, Maiter D. Treatment of adult growth hormone deficiency: who, why and how? A review. Acta clinica Belgica. 2010: 65: 13-22.
- Giustina A, Barkan A, Chanson P, Grossman A, Hoffman A, Ghigo E, Casanueva F, Colao A, Lamberts S, Sheppard M, Melmed S. Guidelines for the treatment of growth hormone excess and growth hormone deficiency in adults. Journal of endocrinological investigation. 2008: 31: 820-838.
- Molitch ME, Clemmons DR, Malozowski S, Merriam GR, Vance ML. Evaluation and Treatment of Adult Growth Hormone Deficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocr Metab. 2011: 96: 1587-1609.
- Tanaka T, Tachibana K, Shimatsu A, Katsumata N, Tsushima T, Hizuka N, Fujieda K, Yokoya S, Irie M. A nationwide attempt to standardize growth hormone assays. Horm Res. 2005: 64: 6-11.
- Thorner MO. Statement by the Growth Hormone Research Society on the GH/IGF-I axis in extending health span. The journals of gerontology Series A, Biological sciences and medical sciences. 2009: 64: 1039-1044.
- Yuen KCJ, Biller BMK, Molitch ME, Cook DM. Is Lack of Recombinant Growth Hormone (GH)-Releasing Hormone in the United States a Setback or Time to Consider Glucagon Testing for Adult GH Deficiency? J Clin Endocr Metab. 2009: 94: 2702-2707.
- Adult Growth Hormone Deficiency Explained: http://www.hgfound.org/res_aghd.explained.html