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Serum Cortisol Rhythmicity

Meaning

Serum Cortisol Rhythmicity refers to the predictable, cyclical pattern of cortisol concentration in the blood serum over a 24-hour period, which is a critical output of the hypothalamic-pituitary-adrenal (HPA) axis and a key component of the circadian rhythm. A healthy rhythm is characterized by a sharp peak shortly after waking, followed by a gradual decline throughout the day, reaching its nadir around midnight. Clinically, assessment of this rhythm is essential for diagnosing HPA axis dysregulation, as a flattened, inverted, or erratic curve is associated with chronic stress, sleep disorders, and various metabolic disturbances. This pattern is a vital indicator of systemic hormonal balance.