Can glucagon stimulation test replace insulin tolerance test for evaluating adult growth hormone deficiency?
Medically reviewed by Louis-Antoine Mullie, MD.
Answer
The glucagon stimulation test (GST) can be considered as an alternative to the insulin tolerance test (ITT) for evaluating adult growth hormone deficiency (AGHD) in certain circumstances, but it does not completely replace the ITT.
Insulin tolerance test (ITT)
- The ITT is considered the gold standard test for establishing the diagnosis of AGHD, using a peak growth hormone (GH) cut-point of 5 mcg/L
- However, the ITT is used less frequently due to safety concerns, laboriousness, the potential to cause severe hypoglycemia, and contraindications in certain patients, such as elderly patients and patients with seizure disorders and cardio/cerebrovascular disease
Glucagon stimulation test (GST)
- The GST can be considered if the ITT is contraindicated or not feasible
- The GST is also recommended if GH-releasing hormone is not available and performance of an ITT is either contraindicated or not practical in a given patient
- The GST should use BMI-appropriate GH cut-points to reduce the possibility of misclassifying GH-sufficient patients because increased BMI is associated with decreased glucagon-induced GH stimulatory effect
Other alternatives
- The growth hormone-releasing hormone and arginine (GHRH+Arg) test is a promising alternative to the ITT for diagnosis of AGHD
- The macimorelin stimulation test is also considered for AGHD, using the GH cut-point of 2.8 mcg/L to differentiate patients with normal GH secretion from patients with GHD
In conclusion, while the GST can be used as an alternative to the ITT in certain situations, it does not completely replace the ITT for evaluating AGHD. Other tests such as the GHRH+Arg test and the macimorelin stimulation test are also viable alternatives. The choice of test should be individualized based on the patient's specific circumstances and the availability of the tests.