Additional Pituitary Function Testing
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Pituitary Tumor & Neuroendocrine Disorders
Pituitary hormones are released in pulses, levels fluctuate during the day, and the release of one hormone directly affects the release of others. For these reasons, a single blood test often is not sufficient to determine the nature and extent of a specific type of pituitary deficiency. Effective assessment tests include the following:
Cortrosyn Stimulation Test
- Adrenocorticotropic hormone (ACTH) is injected to stimulate the adrenal glands and blood cortisol level is checked 60 minutes later.
- When pituitary disease impairs ACTH production, the adrenal glands lose their capacity to secrete cortisol in response to stimulation.
Metyrapone Test
- This test also assesses pituitary ACTH hormones. Twelve tablets (3 grams) of metyrapone are given to the patient at bedtime and blood is drawn the following morning to check ACTH levels.
- Since metyrapone blocks adrenal hormone production, normal individuals respond by producing large amounts of ACTH. Lack of response indicates pituitary disease affecting ACTH production.
Insulin Tolerance Test
- In this test, insulin is injected to lower blood sugars (hypoglycemia).
- The normal response to hypoglycemia is release of ACTH and growth hormone (GH), which counteracts low blood sugars. Patients deficient in GH and ACTH fail show no hormonal response to hypoglycemia.