Cortisol is the main glucocorticoid hormone produced by the adrenal glands and is often referred to as the “stress hormone.” It plays a crucial role in regulating metabolism, immune response, blood pressure, and the body’s ability to respond to physical and emotional stress. Cortisol follows a daily rhythm, peaking in the early morning to support wakefulness and gradually declining throughout the day. Measuring total cortisol in blood reflects the combined amount of free and protein-bound cortisol, providing insight into adrenal activity and overall hormone balance. Abnormal cortisol levels may be associated with conditions such as adrenal insufficiency, Cushing’s syndrome, chronic stress, or metabolic disorders.