Update on the diagnosis of GH deficiency in adults

GH deficiency (GHD) in adults is associated with considerable morbidity and mortality. The diagnosis of GHD is generally straightforward in children as growth retardation is present; however, in adults, diagnosis of GHD is often challenging. Other markers are therefore needed to identify adults who have GHD and could potentially benefit from GH replacement therapy. Consensus guidelines for the diagnosis and treatment of adult GHD recommend provocative testing of GH secretion for patients who have evidence of hypothalamic-pituitary disease, patients with childhood-onset GHD, and patients who have undergone cranial irradiation or have a history of head trauma. Suspicion of GHD is also heightened in the presence of other pituitary hormone deficits. Tests for GHD include measurement of the hormone in urine or serum or measurement of stimulated GH levels after administration of various provocative agents. The results of several studies indicate that non-stimulated serum or urine measurements of GH levels cannot reliably predict deficiency in adults. Although glucagon and arginine tests produce a pronounced GH response with few false positives, the insulin tolerance test (ITT) is currently considered to be the gold standard of the GH stimulation tests available. Unfortunately, the ITT has some disadvantages and questionable reproducibility, which have prompted the development of several new tests for GHD that are based on pharmacological stimuli. Of these, GH-releasing hormone (GHRH) plus arginine and GHRH plus GH-releasing peptide (GHRP) appear to be reliable and practical. Thus, in cases where ITT is contraindicated or inconclusive, the combination of arginine and GHRH is an effective alternative. As experience with this test as well as with GHRH/GHRP-6 accumulates, they may supplant ITT as the diagnostic test of choice.