Validating the Concept:

Is there literature support for measuring diurnal free cortisol in urine? Jerjes (2005, 2006) studied the diurnal pattern of free cortisol in chronic fatigue patients in both saliva and urine, finding very good agreement

Urine collections have the added value of representing at least two hours of time for each collection. This makes them less influenced by transitory shifts in cortisol levels due to acute minor stressors.