Adult growth hormone deficiency syndrome: a personal approach to diagnosis, treatment and monitoring

GH therapy in adult GH deficiency: a review of treatment schedules and the evidence for low starting doses

Recombinant human GH has been licensed for use in adult patients with GH deficiency (GHD) for over 15 years. Early weight- and surface area-based dosing regimens were effective but resulted in supraphysiological levels of IGF1 and increased incidence of side effects. Current practice has moved towards individualised regimens, starting with low GH doses and gradually titrating the dose according to the level of serum IGF1 to achieve an optimal dose. Here we present the evidence supporting the dosing recommendations of current guidelines and consider factors affecting dose responsiveness and parameters of treatment response. The published data discussed here lend support for the use of low GH dosing regimens in adult GHD. The range of doses defined as 'low dose' in the studies discussed here (∼1-4  mg/week) is in accordance with those recommended in current guidelines and encompasses the dose range recommended by product labels.

Physical activity or food intake prior to testing did not affect the reproducibility of GH secretion elicited by GH releasing hormone plus GH-releasing hexapeptide in normal adult subjects

OBJECTIVE

Growth hormone deficiency (GHD) in adults is a defined syndrome of which the adverse effects on different areas of body function are reversed under replacement therapy with GH. The diagnosis of GHD is controversial in adults, relying on the GH secretion elicited by the so-called provocative tests of GH reserve. Most of the tests in use, including the widely employed insulin tolerance test, have been shown to be blunted after daily activities, such as mild exercise, heat or food intake, which makes stringent testing conditions mandatory in order to assure reproducibility. The combined administration of GH releasing hormone (GHRH) and GH-releasing hexapeptide (GHRP-6) is a very effective test for the diagnosis of GH deficiency in adults. In the present study, the perturbatory action of mild physical activity and food intake on the reproducibility of this combined test was assessed.

METHODS

Seventeen healthy volunteers of both sexes were tested twice on separate occasions with the sequential administration of GHRH (90 microg i.v.) plus GHRP-6 (90 microg i.v.) as bolus. Eleven subjects underwent the first combined test in the morning under basal conditions and the second test was performed in the afternoon of the same day after a morning of habitual working activity and after a standard lunch. Another group of six subjects underwent similar double testing in the morning and in the afternoon after morning activity followed by lunch; however, both tests were separated by a period of 6 months.

MEASUREMENTS

GH levels were analysed by time-resolved fluoroimmunoassay, with sampling every 15 minutes.

RESULTS

The reproducibility of the GHRH + GHRP-6 test performed on the same day was high, with the mean GH peak being 65.4 +/- 8.0 microg/l in the basal state and 51.2 +/- 9.6 microg/l after lunch, while the area under the curve (AUC) was 2287 +/- 288 microg/l per 45 minutes in the morning and 1759 +/- 350 after lunch. When a period of 6 months had elapsed between the first and the second test, the reproducibility was well maintained with a mean GH peak of 42.7 +/- 6.2 microg/l in the basal state and 34.3 +/- 3.6 microg/l in the after lunch test, with the AUC 1463 +/- 209 and 1164 +/- 106 microg/l per 45 minutes in the morning and after lunch, respectively. When analysed individually, physical activity, lunch or time elapsed between the two tests did not significantly change the GH peak in the subjects tested.

CONCLUSIONS

The GHRH + GHRP-6 test of GH reserve is a highly reproducible test in adult subjects over time, and is not perturbed by common daily activities, such as mild physical exercise or food intake. Considering that stringent testing conditions are not required and the whole test may be performed in 30 minutes, it may be useful in the clinical setting for the diagnosis of GH deficiency in adults.