The Diurnal Cortisol Test evaluates cortisol levels at multiple times throughout the day to provide information about the body's daily cortisol pattern. Cortisol naturally follows a circadian rhythm, generally changing from higher levels in the morning to lower levels later in the day. Measuring cortisol at different times can provide a broader picture than a single measurement. Testing may be considered when evaluating concerns related to stress, sleep patterns, energy levels, or adrenal hormone regulation. A Diurnal Cortisol Test should be interpreted by a qualified healthcare professional because cortisol levels can be influenced by medications, illness, sleep, stress, and collection timing.