Adrenocorticotropin and corticotropin-releasing hormone tests in preterm infants

The short ACTH test is used in evaluating the hypothalamo-pituitary-adrenal axis (HPA-axis) in preterm neonates after dexamethasone treatment. This te st mainly examines primary adrenal suppression but is also used as a method to test secondary adrenal insufficiency because long-term deprivation of A CTH causes atrophy of the adrenal cortex. The CRH test, on the other hand, directly examines the function of the pituitary. We tested 18 infants in th e neonatal intensive care unit with both the ACTH test and the CRH test to determine which of these two tests more reliably demonstrates HPA-axis supp ression. One patient had normal responses both in the ACTH test and in the CRH test when the limit of 360 nmol/L was used as a sign of proper cortisol secretio n. In four cases the patients' cortisol secretion would have been regarded as normal by the low-dose ACTH test, whereas the CRH test did not show an a dequate cortisol response. In conclusion, the ACTH test did not reliably indicate HPA-axis suppression after a short (<2 weeks) course of dexamethasone therapy in this study. Th erefore, whether the infant is or will he under acute stress after short gl ucocorticoid treatment, ensuring adequate cortisol secretion with the CRH t est should he considered.