Timing of peak serum cortisol values in preterm infants in low-dose and the standard ACTH tests.

The low-dose ACTH test seems to reveal mild cases of adrenal insufficiency and is beginning to be preferred over the standard ACTH test in the evaluation of adrenal suppression both in infants and in adults. The concentration-time profile of plasma cortisol in infants after a low ACTH dose is obscure. In this crossover study, we compared timing of the peak values in the low-dose and the standard ACTH stimulation tests in preterm and full-term infants. We performed the standard ACTH tests (250 microg/1.73 m2) and the low-dose ACTH tests (1 microg/1.73 m2) on 10 infants (26-40 wk gestational age) and measured serum cortisol concentration at 0, 30, 40, 60, and 120 min by RIA. Nine of the infants had received postnatal glucocorticoid treatment, and most of them had also been treated with dexamethasone antenatally. In the low-dose test, the peak values occurred at 30 or 40 min in 9/10 patients. In the standard-dose test, the peak values occurred at 60 or 120 min in 8/10 patients. These results are comparable with those from adults. According to this study, blood samples for the low-dose ACTH test in infants should be taken before dosing and between 30 and 40 min after dosing.