Insulin Tolerance Test

Indications

Assess the HPA axis in patients suspected to have secondary (central) adrenal insufficiency.
Rule out growth hormone deficiency.

CAD or arrhythmia.
Stroke or seizure disorder.
Age > 60 or < 18.
Morning cortisol < 100 (as it may lead to severe and prolonged hypoglycemia, and the insulin tolerance test is likely not required to confirm adrenal insufficiency).

The test should be performed in a monitored setting by a qualified physician or nurse, and the patient should be observed throughout the test.
Make sure that you have the following available to treat complications:
- IV hydrocortisone
- IV dextrose 50%
The patient should be instructed not to drive a car after the test. Transportation should be planned in advance.
The patient should have a meal available to them to consume after the test is performed.

Insert an IV line.
Obtain baseline glucose, cortisol and growth hormone levels.
Administer regular insulin 0.1 units / kg iv bolus followed by a saline flush.
Obtain glucose, cortisol and growth hormone levels every 20 minutes.
Once glucose is < 2.2 mmol/L and the patient has symptoms of hypoglycemia, administer 25 mL (half an ampule) of 50% dextrose, intravenously.
The patient should have a glucose level > 4 mmol/L before leaving the testing centre.

ACTH levels may also be measured.
If you suspect severe cortisol and/or GH deficiency and still want to proceed with the test, consider using a lower insulin dose (e.g., 0.05 units/kg).
If you suspect insulin resistance (e.g., type 2 diabetes), consider using a higher dose (e.g., 0.15 units/kg).
At 40 minute, if the patient does not have symptoms of hypoglycemia and blood glucose remains > 3.5 mmol/L, consider giving a second dose of insulin at 0.05 units / kg (an additional 50% of the initial dose).

Hypothyroidism may impair the cortisol response. If the patient was hypothyroid at the time of the test, consider repeating the test after adequate thyroid hormone replacement.