A clinical diagnostic procedure that assesses the dynamic, 24-hour pattern of cortisol secretion, moving beyond a single point-in-time measurement to evaluate the integrity of the Hypothalamic-Pituitary-Adrenal (HPA) axis. This analysis specifically tracks the Cortisol Awakening Response (CAR) and the diurnal slope, which reflect the body’s capacity to respond to stress and maintain circadian alignment. Deviations from the expected rhythm, such as a flattened or inverted curve, are key indicators of chronic stress adaptation or adrenal dysregulation.
Origin
The concept is rooted in chronobiology and endocrinology, dating back to the mid-20th century when the circadian nature of corticosteroid secretion was first established. The development of non-invasive, multi-point collection methods, particularly salivary cortisol testing, in the late 20th century allowed for the practical clinical application of this rhythmic analysis. This technique offers a functional assessment of stress physiology, superior to static blood tests.
Mechanism
Cortisol secretion is tightly regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus, which drives the HPA axis to release the hormone in a pulsatile, diurnal pattern. The analysis functions by comparing an individual’s measured rhythm—typically high in the morning and gradually declining throughout the day—against established normative ranges. A dysregulated rhythm suggests chronic allostatic load, impairing immune function, sleep quality, and metabolic homeostasis due to persistent or inappropriate glucocorticoid signaling.
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