What is a Diurnal Cortisol Test?

A diurnal cortisol test measures your cortisol levels several times throughout the day, typically after you wake up, before you eat lunch, before you eat dinner, and before you go to bed. By taking more than one sample, the test shows changes in your cortisol levels over time.

Diurnal cortisol tests help healthcare professionals learn more about your endocrine system, which controls hormone secretions. Doctors often use cortisol testing to diagnose problems with the adrenal gland, which produces cortisol.

It can also help diagnose pituitary gland disorders. The pituitary gland produces adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to make and secrete cortisol.