Cortisol (COR) in the Evening

Cortisol (COR) is the main glucocorticoid produced in the adrenal cortex. Cortisol concentration is most often tested in diagnosing diseases caused by excessive cortisol production during Cushing's syndrome, adrenal steroid deficiency during Addison's disease, and for treatment monitoring. Increased serum concentration is found during stress response, psychiatric disorders, obesity, diabetes, alcoholism, and pregnancy, which can cause diagnostic difficulties in the case of Cushing's syndrome. Low cortisol concentration is found in patients with rare adrenal enzyme deficiencies and those under prolonged stress. Normally, the highest cortisol secretion occurs in the second half of the night, with the peak cortisol concentration reached early in the morning. Afterwards, cortisol concentration begins to decrease during the day, reaching the lowest concentration in the first half of the night. Therefore, when taking cortisol samples, circadian variations in cortisol secretion and the impact of stress should be considered.