Nelson writes : "Laboratoiy .findings (for Cushing Syndrome)" Cortisol levels in blood are normally elevated at 8 AM and decrease to less than 50% by midnight except in infants and young children in whom a diurnal rhythm is not always established. In patients with cushing syndrome this circadium rhythm is lost, and cortisol levels at midnight and 8 AM are usually comparable. Obtaining diurnal blood samples present logistical difficulties as part of an outpatient evaluation, but cortisol can be measured in saliva samples, which can be obtained at home at the appropriate times of day. Night time salivary cortisol levels are elevated and may be a screening test in obese children.