The cortisol test measures the level of cortisol, a hormone crucial for stress response, metabolism, and immune function. Cortisol levels fluctuate throughout the day in response to stress and regulate various physiological processes. Elevated cortisol levels may indicate conditions like Cushing’s syndrome, chronic stress, or adrenal tumours, leading to symptoms such as weight gain, high blood pressure, insomnia, and mood swings, while low levels may suggest adrenal insufficiency, Addison’s disease, or hypopituitarism, resulting in fatigue, weakness, dizziness, and weight loss.