ACTH Suppression Test
Function of ACTH
ACTH or adrenocorticotrophin is a secretion from the pituitary gland, a tiny gland at the base of the neck. The quantities of this secretion are generally regulated by the amount of cortisol present in the blood plasma. When ACTH is secreted, it signals the adrenal glands (tiny glands next to the kidneys) to produce more cortisol.
Cortisol regulates blood pressure, cardio-vascular functions, as well as the body’s use of proteins, carbohydrates and fats. Psychological stress or physical trauma causes the cortisol levels to rise. This causes greater breakdown of muscle protein, releasing amino acids into the bloodstream. The liver synthesizes these amino acids to produce glucose for more energy, to help the body cope with the extra stress. This raises the blood sugar level in the body. Too much cortisol in the blood on a permanent basis is harmful as it causes the body to be in ‘fight mode’ and leads to higher blood sugar levels.
If cortisol levels in plasma increase, the secretion of ACTH is suppressed. If cortisol levels decrease, ACTH increases.
Reasons for ACTH Test
ACTH regulates the levels of cortisol in the blood. But in case, either the adrenal gland or pituitary gland is abnormal or malfunctioning, the production of ACTH is suppressed. The ACTH test helps to diagnose the problem.
The suppression test measures how the adrenal glands respond to ACTH. A synthetic steroid called Dexamethasone is administered and the level of cortisol is monitored to see whether it has decreased in response.
Procedure to Conduct ACTH Test
Firstly, dexamethasone, a synthetic steroid, which is similar to cortisol, and also suppresses ACTH, is administered. There are 2 methods of ACTH test: the 6-day method and the rapid method.
• In the 6-day method, urine is collected over 6 days at 24-hour intervals, and the levels of cortisol are measured. On day 3, a low dose of dexamethasone is given orally every 6 hours over a period of 24 hours. On day 5, a higher dose of dexamethasone is given, and the urine is tested on the sixth day.
• In the rapid method, a dosage of usually 1 mg of dexamethasone is given at 11 at night, and at 8 the following morning, blood is drawn and tested for cortisol levels.
Preparation for ACTH Test
• You will be advised to stop any other drugs like contraceptives, cortisteroids, barbiturates or tetracycline.
Risks Involved in ACTH Test
• You might feel a pricking or stinging sensation when the needle punctures your skin.
• There may be excessive bleeding.
• You may feel faint or dizzy.
• There is a slight risk of infection or accumulation of blood at the puncture site.