Cortisol awakening response: are sampling delays of 15 minutes acceptable?

Cortisol awakening responses (CAR) are often blunted or even extinguished when saliva samplings are delayed. The literature suggests that delays of 10 or 15 min are tolerable. Delays of 15 min were analysed with 510 CARs with the first sample taken within 3 min post-awakening followed by 4 samples taken 15, 30, 45, and 60 min later. Varying delays of up to 30 min were analysed with these and further 148 CARs where sampling began within 30 min post-awakening. Times of awakening and of saliva collection were verified by polysomnography or actimetry and by electronic devices respectively. Simulated sampling delays of 15 min revealed highly significant deviations from correctly taken CARs. No deviations were found for delays of up to 11.5 min suggesting that delays of up to 10 min are acceptable but that delays between 10 and 15 min might become critical.