An ACTH test measures ACTH, a hormone secreted from the anterior pituitary gland in the brain.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a band is placed around the upper arm to cause a vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The band is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

The levels of ACTH vary with the body's circadian rhythms (the pattern of physiologic changes that occurs on a 24-hour cycle). This test is most accurate if it is performed early in the morning.

The health care provider may advise you to stop taking steroid drugs and to be at the laboratory or office where the blood is being drawn by or before 8 a.m.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.