ACTH
What it measures, and what changes the number.
ACTH (adrenocorticotropic hormone) is a hormone released by the pituitary gland at the base of the brain. Its job is to signal the adrenal glands to make cortisol. The test measures the amount of ACTH in plasma.
It is almost always interpreted together with cortisol drawn at the same time, because the two form a feedback loop: looking at both shows whether the pituitary signal and the adrenal response match. Urinary free cortisol and other adrenal steroids are sometimes added.
ACTH has a strong daily rhythm and responds quickly to physical or emotional stress, so the time of the draw is recorded and morning samples are common. The hormone breaks down fast outside the body, so blood is usually collected in a chilled EDTA tube and separated promptly; poor handling can lower the measured amount. Reports may call it ACTH, PLASMA, corticotropin or adrenocorticotropic hormone.
Often read alongside: Cortisol, Urinary free cortisol (24h), DHEA-S, 17-OH progesterone