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Diagnostic Hormone Testing
Pituitary tumors can affect the pituitary gland's ability to produce hormones. These hormones in turn affect how other glands work and produce hormones. Hormone testing is an essential and challenging dimension of diagnosing pituitary tumors and disorders.
Hormone testing helps:
- Rule out that the symptoms a person is experiencing are caused by other conditions than a pituitary tumor or disorder
- Identify how the pituitary gland is being affected by a tumor
- Establish appropriate medical action such as drug therapy to cause the pituitary gland to produce more - or less - of a particular hormone
- Identify hormones that may need to be replaced
The pituitary gland controls the activity of most other glands in the body. The pituitary gland itself produces:
- Adrenocorticotropic hormone (ACTH). This hormone triggers the adrenal glands to release cortisol. When too much is produced, Cushing's disease results. When there's too little ACTH - and thus too little cortisol circulating in the body - adrenal insufficiency results.
- Growth hormone (GH). As its name suggests, this hormone causes the body to grow during childhood and adolescence. It triggers the liver to produce IGF-1, which stimulates muscle and bone changes. When there is too much growth hormone in the body, it causes acromegaly (in adults) or gigantism (in children). Too little GH causes growth hormone deficiency.
- Prolactin. This hormone stimulates a woman's breasts to produce milk after a baby is born.
- Thyroid-stimulating hormone (TSH). This hormone causes the thyroid to release thyroid hormone. Too much thyroid causes hyperthyroidism; too little thyroid causes hypothyroidism.
- Follicle-stimulating hormone (FSH). This hormone in women causes eggs to be released in the ovaries and in men causes sperm to be produced.
- Luteinizing hormone (LH). This hormone causes an egg in a woman's ovary to be released to the uterus during her monthly cycle. In men, the hormone causes the testicles to release testosterone.
While hormone testing most often requires a blood sample, the process of getting an accurate measure of a particular hormone can be complex. Many hormones have natural highs and lows that vary during the time of day or night.
Provocative/Suppressive Lab Tests
Certain hormone tests (stimulation / suppression tests) are done while hormones or other drugs are used to artificially stimulate or stop the body from producing a particular hormone to judge the body's reaction. These tests include:
Growth Hormone Deficiency Tests
- To measure growth hormone response to glucagon: This test measures whether or not you have growth hormone deficiency. Glucagon is administered intramuscularly. Growth hormone levels are measured every half hour over four hours.
Cortisol Deficiency Tests
- To measure cortisol response to ACTH stimulation: ACTH is given through a vein into the blood stream. The amount of cortisol in the blood stream is measured after a period of time.
- To measure cortisol response to hypoglycemia (low blood sugar): patients receive insulin through a vein. This causes low blood sugar to stimulate ACTH and cortisol secretion. Cortisol levels are measured every 30 minutes for two hours.
Test to Diagnose Acromegaly
- Oral glucose tolerance test: A patient is given a sweet drink containing 75 grams of glucose (sugar). Sugar in the blood stream lowers the level of growth hormone. The amount of growth hormone in the blood is measured two hours after drinking the sweet beverage. Patients with acromegaly will not have a drop in the growth hormone levels in their blood.
Tests to Diagnose Cushing's Disease
- Dexamethasone suppression test: A dexamethasone tablet is taken at 11 p.m. the night before the test. The following morning, the amount of cortisol in the blood is measured.
- Bilateral Inferior Petrossal Sinus Sampling (IPSS): Catheters are introduced into the groin and gradually advanced via the venous system into the inferior petrossal sinuses, spaces inside the brain around the pituitary gland. An injection of corticotrophin-releasing hormone (CRH) is given. Blood is drawn from the catheters and from a vein in the arm and compared.