Insulin Tolerance Test: A Must Know: ITT: How is the test done?

What to avoid?

There are certain situations wherein the test is not applicable for it could cause harm to their health or it may produce an erroneous result. These are:

Persons who have epilepsy, heart problems, or untreated hypothyroidism
Avoid vigorous exercise for this may produce an erroneous result
Patient should fast for 8 hours

Before the test, the patient should have the knowledge on the procedure being done. The patient should be warn on the possible side effects that may happen. Since hypoglycemia will happen, the patient must be observed for the tendency of fainting. After the test, the patient must be properly taken cared of by observing the punctured site for bleeding and giving something to eat to compensate for the induced hypoglycemia.

What to expect during the test?

1. The patient should be lying on the bed.

2. On the vein of the arm, the clinician will place a small tube used for collecting blood samples (cannula) and measure the growth hormone, cortisol and glucose concentration.

3. Patients must be hypoglycemic. So, clinician would induced hypoglycemia by giving insulin to the patient. The insulin will cause stress to the body that will stimulate the production of growth hormone and cortisol.

4. The blood glucose level should be <2.2 mmol/L. If the insulin produced no effect on the blood glucose level, a second dose of insulin may be given.

5. The blood glucose level should be monitored throughout the test.

6. After 1-2 hours, the clinician should take blood to know the concentration of growth hormone and cortisol.

7. The clinician will monitor you for possible side effects and give something to eat to compensate for the induced hypoglycemia.

What to know more?

When there is a decrease level of glucose in the blood (hypoglycemia), the Hypothalamus will stimulate the production of Cortisol Releasing Hormone (CRH), then the CRH will stimulate the release of Adrenocorticotropin Hormone (ACTH) then the adrenl cortex will release Cortisol. In this test, we are measuring the levels of the Cortisol that is responding in our body during decrease levels of glucose.

Same as with the Growth hormone. If the body is put under stress (i.e hypoglycemia), the Hypothalamus will stimulate the production of Growth Hormone Releasing Hormone (GHRH) to stimulate the release of Growth hormone by the Anterior Pituitary.

A normal cortisol response will rise to 580 nmol/ L or more while a normal growth hormone response must increase to more than 20 mU/L. Results under and over the normal values indicate abnormal production or function of Adenocorticotropin hormone (ACTH) and/or Growth hormone.

These abnormal findings may indicate:

Cushing's Syndrome

Also known as hypercortisolism, a disease wherein there is elevated cortisol levels in the patient’s result. It is caused by taking long-term medications in conditions like Asthma, Rheumatoid Arthritis, and other inflammation containing the hormone (Cortisol).

Hypopituitarism

It is a disease caused by the under production or failure production of the hormones of pituitary gland. The pituitary gland has short supply of pituitary hormones thus affecting the body's routine function such as blood pressure, growth and reproduction. Symptoms may include fatigue, weight loss, decreased sex drive, decreased appetite, facial puffiness and short stature in children.

References:

Brook, Charles, et. al, Brook’s Clinical Pediatric Endocrinology, 6^th edition, page 141

Pagana, Kathleen D., et. al., Mosby’s Diagnostic and Laboratory Test Reference, page 495

Warrel, David A., et. al., Oxford Textbook of Medicine, 4^th edition, page 195

http://www.mayoclinic.org/diseases-conditions/hypopituitarism/basics/symptoms/con-20019292

http://medical-dictionary.thefreedictionary.com/Cushing's+syndrome