Pituitary Tests

Here’s a quick summary of tests your doctor may request to test your pituitary function. Some are simple tests that can be requested by your General Practitioner and some are more complex and carried out by an Endocrinologist.

Testing for Adrenocorticotropic Hormone (ACTH) Deficiency

  • Insulin Tolerance Test (ITT) also called Insulin Stress Test is the “gold standard” test. The test involves lowering blood glucose with the hormone insulin and measuring through blood samples how much cortisol is produced from the adrenal glands in response to that stress on the body. The hypoglycaemia is sensed at the hypothalamus so this tests the integrity of the whole axis. There are some contraindications to this and so you may be offered a different test if required.

  • Metyrapone test –an alternative where an Insulin Tolerance Test (ITT) is contraindicated.

    For this test you spend the night in hospital. At midnight you’re given a tablet containing Metryrapone along with a snack. In the morning, you will have a blood test between 8 am and 9 am to test the response of your HPA axis.

  • Glucagon stress test – an alternative where an Insulin Tolerance Test (ITT) is contraindicated.

    For this test you’re in the unit for the day from 9 am. You’ll have a cannula (a small needle) inserted into a vein in your arm. You’ll have blood tests before and at intervals after being given an injection of glucagon. The blood tests measure the response of your HPA axis and also your Growth Hormone.

Testing Adrenal gland function

  • Short Synacthen test - You may be offered this test to see if your Adrenal glands can release the hormone Cortisol when stimulated. In many patients it can give information that is almost as reliable as an insulin or glucagon stress test. It is safer, quicker, more available and reproducible.

    A synthetic form of ACTH is given to you via an injection. The response of your adrenal glands is then measured via a blood test. It therefore does not test the whole axis, but this does not matter in most cases, the information can still be useful.

Monitoring cortisol levels

  • Blood test: your doctor may request serum cortisol tests to monitor your cortisol levels. Sometimes several of these tests are taken throughout a day, known as a cortisol day curve. This is to give a picture of your cortisol levels through the day. This is usually to monitor glucocorticoid replacement, for example hydrocortisone tablets.

Testing for Thyroid Stimulating Hormone (TSH) deficiency

  • Blood test: Your TSH levels and free thyroxine can be measured in a routine blood test, usually carried out in your hospital phlebotomy department, your GP practice or in a community blood test unit.

  • Some thyroid function tests only measure TSH routinely.

  • If there is secondary thyroid insufficiency (from hypopituitarism) then measuring TSH alone will not necessarily help.

  • Free thyroxine (T4) must be measured alongside the TSH.

  • This is sometimes supported by a free triiodothyronine test (T3). This test can be difficult to interpret because the conversion of thyroxine (T4) into triiodythyronine (T3) occurs mostly in the cells of the body.

Testing for Follicle Stimulating Hormone (FSH) & Luteinising Hormone (LH) deficiency

This involves a routine blood test to check the levels in your blood. Your hospital laboratory will have reference intervals for each part of the menstrual cycle.

Testing for Growth Hormone Deficiency

  • An Insulin Tolerance Test (ITT) is the “gold standard” test for growth hormone deficiency. This involves lowering blood glucose levels with insulin and taking blood tests to measure the response to this stress. There are contraindications for this test and so you may be offered a different test.

  • A GHRH-Arginine Test is another way to measure growth hormone. GHRH is the hormone from the hypothalamus that usually stimulates the pituitary to release growth hormone. In this test a synthetic version of GHRH is given to you via injection. The response from your pituitary gland is then measured in blood tests. This test has less contraindications compared to the ITT; however, it can also be less reliable.

  • Glucagon stress test – an alternative where an Insulin Tolerance Test (ITT) is contraindicated.

  • It can be difficult to accurately measure your Growth Hormone levels in a routine blood test, so IGF-1 is measured instead. This is how your Growth Hormone levels will be monitored if you start on replacement medication.

  • A newer test, known as the Macrilen or Macimorelin test has also recently been approved in the USA.

Testing for prolactin

Your doctor may request a blood test to measure your prolactin.

Testing for Melanocyte Stimulating Hormone (MSH)

MSH levels in the blood can be measured in a blood test, however it is not commonly tested for.

Oxytocin deficiency or excess

Currently there are no routine tests for this.

Testing for Anti-Diuretic Hormone (ADH) deficiency

  • Serum osmolality and urine osmolality test measures levels of fluid in the blood compared to fluid levels in the urine.

  • A water deprivation test may be carried out in hospital to confirm a diagnosis of AVPD. This starts in the early morning and continues through the day. You are not able to drink or have any fluids throughout the test. Blood and urine samples are taken each hour to compare their concentration / osmolality. Blood pressure, body weight and urine volume passed are also measured.

  • AVDP is confirmed if the blood osmolality increases beyond a certain level but the urine fails to concentrate. If the urine concentration defect then corrects with the addition of ADH (given by injection as part of the test) cranial AVDP is confirmed.

  • This test is difficult and generally only done by doctors, and in centres, with some experience of arranging and interpreting it.

 

Other tests

Your doctor may sometimes also request these tests to get an overall picture of your health:

  • Cholesterol

  • Diabetes Mellitus

  • Vitamin D

  • Serum Sodium

  • Full Blood Count

  • Bone Profile

  • Liver Function

This summary is intended for general information only. Please refer to your doctor for information and advice specific to you as a patient.

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