The ACTH test is used to assess how well the pituitary and adrenal glands are functioning. ACTH stimulates the adrenal glands to produce cortisol, a vital hormone for stress response, metabolism, and immune function. Abnormal levels may indicate adrenal insufficiency, Cushing’s syndrome, or pituitary disorders. Accurate timing and handling of the blood sample are crucial, as ACTH levels can fluctuate throughout the day.