Aim: To investigate the relationship between baseline and stimulated cortisol responses in relation to the habitual time of rising and time of test.
Method: The self-reported habitual rising time and time of cortisol testing were recorded in 63 consecutive patients (47F, 17M, age 1894) undergoing standard stimulation testing with tetracosactide (SynActhen) 250 μg i.v. In total, 75 tests were analysed. A normal response was defined as a 30 min peak cortisol >450 nmol/l. All tests were performed between 08001300 h.
Results: Of the 75 tests, 65 were classified as normal responses; ten had impaired peak values. In the group with normal responses, Pearsons analysis showed no correlation between baseline and 30 min cortisol responses with habitual rising time or the interval between this time and the time of the test. A weak negative correlation was noted between the baseline cortisol value and the actual time of test irrespective of the time of rising (r: −0.28, P: 0.026). The highest incremental rises were seen in subjects with the earliest time of rising and lowest baseline values (r: −0.58, P: 0.038). In the subgroup with impaired responses, higher peak cortisols were observed in those where the time of test was closest to their usual time of rising (r: −0.66, P: 0.037).
Conclusion: In patients with normal adrenal reserve, peak cortisol responses are not significantly influenced by the timing of the test in the morning or the usual time of rising. In those with impaired cortisol responses, the test time and its relation to the time of rising may influence the incremental cortisol response, although this needs to be confirmed with larger patient numbers. For the majority of patients, adrenal stimulation tests can be reliably performed any time in the morning.