Reference region for parameters of circadian cortisol rhythm in pediatrics

The authors introduce methods for the interpretation of biomedical time series. A total of 25 blood cortisol profiles, sampled from 10 healthy North American men, 16-28 years of age, every 4 h for 24 h across all seasons, serve for the computation of a so-called paradesm, a 90% prediction region for the circadian amplitude-acrophase pair. A statistically significant circadian rhythm is found as the principal spectral feature in cortisol data from 58 Spanish children of short stature, 6-14 years of age, sampled at about 3-h intervals for 24 h. Differences in age, ethnicity, climate, diet, health, and sampling conditions between the two populations notwithstanding, individual estimates of the circadian amplitude and acrophase are inside the reference paradesm for 37 of 42 boys and 12 of 16 girls. The validation of the paradesm used awaits the addition of more data and procedures for nonparametric resampling, such as bootstrapping, when testing this approach further for diagnostic purposes in the clinic