it is clear that serum IGF-1 and or IGFBP-3 can be normal in patients with undisputed GHD
Various investigators have reported normal IGF-1 values in 37–70% of GH deficient adults
The co-administration of arginine and GHRH (the combined test) is a powerful stimulus for GH production and has gained increasing acceptance as a useful method of diagnosing GHD [34]. This test has been advocated as a suitable alternative to ITT
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
ARG plus GHRH test, high sensitivity (96 and 95%, respectively) and specificity (92 and 91%, respectively) for GH deficiency were achieved
The greatest diagnostic accuracy occurred with the ITT and the ARG plus GHRH test
95% specificity could be achieved with the ARG plus L-DOPA and ARG tests only with very low peak GH cut-points (0.25 and 0.21 microg/liter, respectively) and not at all with the L-DOPA test
Although serum IGF-I levels provided less diagnostic discrimination than all five GH stimulation tests, a value below 77.2 microg/liter was 95% specific for GH deficiency
study evaluated 6 tests for HGH deficiency diagnosis. Ninety-five percent specificity found with ARG + l-DOPA and ARG alone. However, the authors found a 95% specificity with IGF-1 < 77. Although, IGF-1 is false negative in up to 65% of those with HGH deficiency.