Laboratory Diagnosis of Growth Hormone Deficiency in Adults

Abstract

Growth hormone deficiency (GHD) is a well-recognized clinical syndrome in adults. The diagnosis, however, can be challenging and is often established through one or more laboratory GH stimulation tests. The decision to perform GH stimulation testing should be based on medical history and clinical findings, using appropriate GH stimulation test(s) for biochemical confirmation. Adults evaluated for GHD should include those with signs and symptoms of hypothalamic-pituitary disease, those who have received cranial irradiation or tumor treatment, and those with a history of traumatic brain injury. Patients with three or more pituitary hormone deficiencies and an IGF-I level below the reference range are the exception, whereas other patients require GH stimulation test(s) to confirm the diagnosis. The insulin tolerance test (ITT) remains the test of choice; however, this test is labor intensive, has significant contraindications, can be unpleasant for the patient, and is potentially hazardous. The GH-releasing hormone (GHRH) plus arginine test was accepted as a safe and reliable alternative to the ITT, but with the discontinuation of Geref® (a GHRH analogue) in the United States in 2008, the glucagon stimulation test has gained popularity as the alternative test to the ITT. Cut points differ across tests and results may be influenced by gender, age, body mass index, and the assay reference preparation. Currently, several synthetic GH secretagogues that mimic ghrelin are in development and may become available for use in the diagnosis of adult GHD in the near future. In this chapter, various GH stimulation tests and potential drawbacks in conducting these tests and future perspectives are discussed.