Insulin Tolerance Test

The insulin tolerance test is the gold standard test for assessing the integrity of the hypothalamo-pituitary-adrenal axis. Stress, in this case hypoglycemia, leads to the secretion of the hypothalamic hormones, growth hormone releasing hormone (GHRH) and corticotrophin releasing hormone (CRH) which in turn stimulate the pituitary to produce GH and ACTH. ACTH production is assessed by the measurement of adrenal cortisol production. This test is dangerous as it relies on the induction of symptomatic hypoglycemia which must be treated immediately if the symptoms become severe.
The patient must be fasted overnight (4 hours for infants), although drinks of water are allowed
Ensure that glucose (10% dextrose) and hydrocortisone are available for i.v. injection if necessary
A glucose drink must be available. This may be ~40g dextrose powder (4 heaped teaspoons) dissolved in approximately half a glass of squash, alternatively POLYCAL or rapilose can be administered.
Child must remain on the ward and eat for at least an hour after the test before the cannula is removed and the patient discharged.
1. Start the test between 0800h and 0900h. Weigh the patient, insert an indwelling cannula and take a basal blood sample (t = -30) for glucose, growth hormone and cortisol. Wait 30 minutes before taking the baseline (t = 0) sample for glucose, growth hormone and cortisol as cannulation may cause GH to rise. The patient should be resting throughout the test.
2. Check glucose level by meter:
If glucose less than3.5 mmol/L do not administer insulin.
If glucose level 3.5 - 4.5 mmol/L then administer half the dose of insulin.
If glucose more than 4.5 mmol/L then continue with the test as indicated.
3. Dilute soluble insulin (Actrapid) with normal saline to give a solution containing 1 unit per ml. Give an i.v. dose of 0.1 units per kg body weight.
This dose should be reduced to 0.05 units per kg in patients who might be unduly sensitive to insulin, such as patients with suspected hypopituitarism, severe malnutrition, or those with a baseline blood glucose between 3.5 and 4.5 mmol/L.
4. Monitor blood glucose closely until adequate hypoglycemia has been established (less than 2.2 mmol/L) or the child shows signs of hypoglycemia (e.g. sweating or drowsiness). Administer glucose drink of ~40 g dextrose powder (4 heaped teaspoons) dissolved in approximately half a glass of squash, or POLYCAL or rapilose can be administered. If there are more severe symptoms of hypoglycemia (e.g. impaired consciousness), i.v. glucose may be required.
5. Take further blood samples for glucose, growth hormone and cortisol at 15, 30, 60 and 90 min post insulin administration.
6. Remember to check the child’s glucose level by meter and the responsiveness at every sample.
Credit:
benzoix @Freepik Company