The 1-μg `low doseʹ ACTH test for assessment of adrenal function in geriatric patients

A commonly utilized dynamic test for evaluation of the hypothalamic-pituitary-adrenal (HPA) axis in the geriatric patient is the standard 250-μg ACTH stimulation test. However, there are significant potential drawbacks associated with this study. In contrast, administration of 1 μg of ACTH has been shown to be very sensitive for detecting abnormalities in the HPA axis. We therefore assessed the responses of two groups of patients (aged 80–95 years) with no evidence of HPA disease using either the 1 or 250 μg dose of ACTH (Synacthen). Twenty six patients received 1 μg of ACTH (Synacthen). Seventeen others received a standard 250 μg dose. Patients were randomly chosen. There were no significant differences in age or sex between the two groups. Plasma cortisol was measured at 30 and 60 min after intravenous administration of either dose of ACTH. No significant statistical differences were noted in plasma cortisol responses to 1 or 250 μg of ACTH. We conclude that the 1 μg `low doseʹ ACTH stimulation test can substitute for the standard 250 μg test. Clinical judgment must be used in conjunction with these tests in formulating therapeutic decisions.