The pituitary—a small, oval gland located at the base of the brain—is sometimes called the master gland because it regulates and controls the secretions of other endocrine glands and various body processes by producing a variety of hormones. Measuring blood levels of the following pituitary hormones can provide valuable information about the function of the pituitary and the other glands controlled by these hormones.

Growth hormone (GH), as its name implies, plays a central role in regulating the body’s growth. If a blood test indicates an elevated level of GH, a GH suppression test, which measures GH levels in response to glucose (a sugar that normally suppresses GH secretion) is done to confirm the finding. If the blood level of GH is low, a GH stimulation test is performed to measure GH levels in response to substances that normally stimulate GH secretion (such as the hormone insulin, the amino acid arginine, or growth hormone-releasing hormone, or GHRH).

Insulin-like growth factor-1 (IGF-1) is not a hormone but a substance secreted by the liver that is often measured to assess GH secretion by the pituitary. GH accomplishes its effects on many tissues through somatomedins, a group of proteins that include IGF-1. Because GH is produced in several bursts during the day and may be affected by a variety of factors such as food intake and exercise, measuring IGF-1 may in fact be a more accurate reflection of average GH levels than a direct blood test.

Prolactin is a pituitary hormone that helps to prepare the mammary glands for lactation during pregnancy and stimulates milk production after a woman gives birth. Prolactin levels are measured in people suspected of having pituitary tumors, which are known to secrete excessive amounts of this hormone.

ACTH, or corticotropin, is a pituitary hormone that stimulates the adrenal gland to release cortisol and other hormones. Measuring ACTH levels in the blood can aid in the diagnosis of adrenal gland abnormalities, such as Cushing’s syndrome (overproduction of cortisol) and Addison’s disease (a form of adrenal insufficiency marked by underproduction of cortisol). To help diagnose Cushing’s syndrome, the dexamethasone suppression test may be performed to measure the effect that dexamethasone, a drug similar to cortisol, has on cortisol levels. Alternatively, to evaluate adrenal insufficiency the ACTH stimulation test is used to measure the adrenal response to ACTH administration.

Luteinizing hormone (LH), produced by the pituitary, acts on the ovary in women and the testis in men. In women, a surge in LH secretion at mid-menstrual cycle causes ovulation and helps to maintain the specialized portion of the ovary that produces the female sex hormone progesterone. In men, LH secretion stimulates specialized cells in the testis to release the male sex hormone testosterone. LH levels are measured in the evaluation of infertility in both women and men.

Follicle-stimulating hormone (FSH) is a pituitary hormone that also helps to control the activity of the ovary and testis. In women, FSH stimulates the development of the ovarian follicles for ovulation. In men, FSH stimulates and helps to maintain sperm production. FSH measurements can aid in the evaluation of infertility and disorders of menstruation.

Purpose of the Pituitary Hormone Tests

Growth hormone and IGF-1 tests:

  • To aid in the diagnosis of acromegaly (a disease marked by enlargement of the bones of the extremities, face, and jaw)
  • To help identify tumors affecting the pituitary or the hypothalamus in the brain
  • To aid in the monitoring of human growth hormone therapy
  • To detect hormone abnormalities
  • To follow-up to other abnormal hormone test results
  • To help evaluate pituitary function
  • To help identify excess or diminished GH production and give the doctor information about the severity of a person's condition
  • To help the doctor figure out why a child is small or growing slowly

Prolactin test:

  • To diagnose and monitor pituitary tumors
  • To evaluate patients with amenorrhea (absence of menstruation) or galactorrhea (abnormal secretion of milk)
  • To determine the cause of headaches and visual disturbances
  • To diagnose erectile dysfunction
  • To diagnose infertility
  • To diagnose, monitor the treatment of or detect recurrence of prolactinomas
  • To evaluate anterior pituitary function (along with other hormones)

ACTH tests:

  • To aid in the diagnosis and evaluation of adrenal abnormalities, such as Addison’s disease and Cushing’s syndrome

LH and FSH tests:

  • To aid in the diagnosis of infertility in both men and women
  • To help evaluate disorders of menstruation, including amenorrhea
  • To determine the onset of menopause
  • To monitor infertility treatments designed to induce ovulation

Who Performs Pituitary Hormone Tests

  • A doctor, a nurse, or a technician

Special Concerns about Pituitary Hormone Tests

  • A wide range of factors—including medications and nutritional supplements, exercise, sleep, stress, nutrition, and the menstrual cycle—may alter the results of the various tests. In particular, these variables cause a significant overlap between normal and abnormal results when GH is measured directly.
  • A nuclear scan performed within the previous week may affect the results of these tests, because pituitary hormones are often measured with a laboratory technique that utilizes a radioactive isotope (radioimmunoassay).
  • Certain individuals, including those with epilepsy, cerebrovascular disease, or a recent heart attack, should not undergo the GH stimulation test because it produces low blood sugar and may cause serious complications.
  • Blood levels of ACTH vary during the day, peaking in the early morning (from 6 to 8 AM) and declining in the evening (from 6 to 11 PM). This pattern differs in people who work nights and sleep during the day; this fact must be taken into account when interpreting the test results.

Before the Pituitary Hormone Tests

  • You may be asked to fast, limit your physical activity, and reduce stress levels for variable periods before these tests.
  • Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain of these agents before the test.
  • Tell your doctor if you’ve had any recent procedures, such as a nuclear scan, that introduce radioactive material into your bloodstream.

What You Experience

Direct blood test for pituitary hormones:

  • A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
  • The blood sample may need to be taken at a specific time during the day.

GH stimulation test:

  • A special type of intravenous (IV) catheter is inserted into a vein in your arm. It allows both administration of medications and withdrawal of blood samples.
  • A blood sample is taken so that pre-test blood levels of GH, glucose, and cortisol can be measured.
  • Arginine, insulin, or GHRH is then infused through the IV line, and blood samples are obtained at several intervals over the next 2 hours.
  • When insulin is used, you will be monitored continuously for signs of hypoglycemia (weakness, restlessness, hunger, sweating, nervousness) and low blood pressure.
  • You may be given ice chips to chew to alleviate thirst.

GH suppression test:

  • Blood samples are drawn between 6 AM and 8 AM using venipuncture to record pre-test GH levels.
  • You are asked to drink a glucose solution. It will taste very sweet. Drink it slowly to avoid nausea.
  • Additional blood samples are drawn at several intervals over the next 2 hours so that they can be analyzed for GH levels in response to the glucose.

ACTH stimulation test:

  • Blood samples are drawn using venipuncture to record pre-test cortisol levels.
  • Less than 30 minutes later, an ACTH analogue (cosyntropin) is injected into a vein, usually in the arm, over a 2-minute period.
  • Blood samples are taken 30 and 60 minutes after the injection so they can be analyzed for cortisol levels in response to cosyntropin.

Dexamethasone suppression test:

  • At 11 PM, you are given 1 mg of dexamethasone by mouth, together with milk or an antacid to prevent gastric irritation.
  • At 8 AM the next morning, blood samples are taken by venipuncture to measure your cortisol level before you arise.
  • If no cortisol suppression is observed, you will be given a higher dose of dexamethasone (8 mg) to suppress ACTH production.

Risks and Complications of Pituitary Hormone Tests

  • Severe hypoglycemia may develop during the GH stimulation test, but this complication is unlikely to occur under close observation.
  • The other tests entail no significant risks.

After the Pituitary Hormone Tests

  • Resume your normal diet and any medications that were withheld before the test, according to your doctor’s instructions.
  • After the GH stimulation test, you will be given cookies and punch or an IV glucose infusion to restore your normal blood sugar levels.
  • After the ACTH suppression test, you will be evaluated for signs of gastric irritation as well as steroid-induced side effects by monitoring your weight, glucose level, and potassium level.
  • Blood may collect and clot under the skin (hematoma) at the site of needle puncture or IV insertion; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.

Pituitary Hormone Test Results

  • Your blood samples are sent to a laboratory for analysis. A physician will review the results for evidence of any pituitary hormone disorder or other problem.
  • If an abnormality is found and the doctor can make a definitive diagnosis, appropriate treatment will be initiated.
  • In many cases, abnormal results on one or more of the pituitary hormone tests will necessitate additional tests to establish a definitive diagnosis.

Source:

The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 30 Jan 2012

Last Modified: 30 Jan 2012