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Hypopituitary adults with GHD have been reported to have normal serum IGF-I levels in 37–70% of patients in various studies (5, 9, 18, 21, 22). This is owing in part to the fact that multiple factors regulate serum IGF-I concentrations including nutritional status; hepatic and renal function; and circulating concentrations of thyroid hormone, androgens, and estrogens

changes in concentrations of IGF-binding proteins (IGFBPs) influence the total concentration of IGF-I in plasma

Among patients with an IGF-I sd score above −1 in the present study, 46% had a peak GH less than 2.5 μg/liter and 67% had a peak GH less than 5 μg/liter.

In summary, adult GHD can be predicted with 95% accuracy by the presence of either three or four PHDs or a serum IGF-I concentration less than 84 μg/liter

We propose that adult patients with three or four PHDs (three or four of the following deficiencies: TSH, ACTH, gonadotropins [LH and/or FSH], and AVP [central diabetes insipidus]) do not require a GH stimulation test to make the diagnosis of adult GHD

The glucagon stimulation test (GST) is a reliable, safe alternative to the ITT in the diagnosis of GHD

An intravenous infusion of arginine (0.5 g/kg body weight) together with an intravenous bolus of GHRH (1 mcg/kg body weight) is administered [30]. Serum samples for GH are then obtained every 15–30 minutes for two hours.

Obesity, particularly marked obesity, is associated with blunted GH secretion in response to provocative stimuli

It has also been suggested that that even mildly increased BMI (25–30 kg/m2) can result in diminished stimulated GH production in 13% of healthy subjects

Corneli et al. have defined BMI-specific cut-off points for diagnosing adult-onset GHD using GHRH + arginine—11.5 ng/mL for those with BMI < 25 kg/m2, 8.0 ng/mL for BMI 25–30 kg/m2, 4.2 ng/mL for those with BMI > 30 kg/m2

GH levels are higher during the luteal phase in comparison with the follicular phase of the cycle

Oral, in contrast to transdermal oestrogen, lowers IGF-1 levels and is associated with increased GH levels

Adequate pituitary replacement with thyroxine and hydrocortisone are needed for optimal GH production

one cannot rely on a low IGF-1 to diagnose GHD in women taking oral oestrogen preparations.

Numerous GH secretagogues are available with the insulin tolerance test being the gold standard and the glucagon stimulation test or the GHRH + arginine as acceptable alternatives

ain et al. found the GST to be at least as good as the ITT in provoking GH secretion

the GST is safe, with almost no contraindications, it causes nausea and sometimes vomiting in 15–20% of subjects