Recommended diagnostic tests for confirming growth hormone deficiency (GHD) in adults primarily involve growth hormone stimulation tests, as basal GH levels are not reliable due to pulsatile secretion. The insulin tolerance test (ITT) is considered the gold standard for diagnosing adult GHD, as it evaluates the pituitary’s capacity to secrete GH in response to hypoglycaemia, which is a potent stimulus NICE NG243.
Alternative stimulation tests include the glucagon stimulation test and the growth hormone-releasing hormone (GHRH) plus arginine test, which are used when ITT is contraindicated or not feasible, such as in patients with seizures or cardiovascular disease NICE NG243. These tests provoke GH secretion through different mechanisms and have been validated for diagnostic accuracy Gabellieri et al. 2010Hazem et al. 2011.
It is important to interpret stimulation test results in the context of clinical features and IGF-1 levels, although IGF-1 alone is insufficient to confirm GHD due to variability and overlap with normal ranges Feingold et al. 2000. Confirmatory testing is recommended when clinical suspicion is high, especially in patients with multiple pituitary hormone deficiencies or known hypothalamic-pituitary disease NICE NG243.
Recent meta-analyses support the high diagnostic accuracy of ITT and glucagon stimulation tests, with GHRH plus arginine also showing good performance, but highlight the need for standardised protocols and cut-off values tailored to assay methods and patient characteristics Hazem et al. 2011.
Key References
- NG243 - Adrenal insufficiency: identification and management
- NG145 - Thyroid disease: assessment and management
- (Gabellieri et al., 2010): Testing growth hormone deficiency in adults.
- (Hazem et al., 2011): The accuracy of diagnostic tests for GH deficiency in adults: a systematic review and meta-analysis.
- (Feingold et al., 2000): Growth Hormone Stimulation Tests in Assessing Adult Growth Hormone Deficiency.