Abstract
Diagnosis of growth hormone deficiency (GHD) involves demonstration of lack of growth hormone (GH) response to a provocative stimulus. The current gold standard is the insulin tolerance test (ITT).
This study evaluated an established alternative to the ITT: stimulation with growth hormone releasing hormone and arginine (GHRH + Arg). It is the first comparison to use a GH assay (Beckman Access) calibrated against the new international standard 98/574. Subjects (n = 69) were randomized to three groups (controls, low probability of GHD and high probability of GHD) and to one of two testing protocols. Subjects rated the acceptability of each test. The study was underpowered and terminated early due to lack of GHRH.
Predictably, significant differences in GH response were seen between the three groups, with the lowest response in those with a high probability of GHD. Response to GHRH + Arg was greater than to ITT but lower than the previously established three-fold difference. A measured response for GHRH + Arg (3.67 μg/L) corresponding to an ITT response of 3 μg/L was found to give the best sensitivity (79%) and specificity (100%). Within-subject repeatability was better for GHRH + Arg. Numbers of adverse events were lower with GHRH + Arg, but more were related to the product than with ITTs. Overall patients preferred GHRH + Arg.
The authors conclude that the GHRH + Arg test represents a viable and more appealing alternative to the ITT. Limited availability of GHRH is a concern with respect to routine use of this test. The use of a standardized GH assay implies that cut-offs derived can be applied to other GH assays with the caveat that they were derived from a small study population.