Insulin Tolerance Test (ITT)

Precautions:

Do not leave the patient unattended since hypoglycemia is expected.

A physician must be available in the walking distance from the room where the ITT is performed.

Interpretation:

A cortisol level <500 nmol/L (18 µg/dL) is consistent with an abnormal HPA axis [1].
A serum growth hormone (5 ng/mL ( 5 mcg/L)) is consistent with severe growth hormone deficiency (96 % sensitivity and 92 % specificity) [2]. To obtain 95 % specificity, a lower peak serum GH cut point at 3 μg/ml (3 ng/ml) may be used [2].

Caveats:

The test should be performed by an experienced clinician
To be able to interpret test results, patients should achieve a glucose level < 2.2 nmol/L (40 mg/dL) associated with symptoms of hypoglycemia including headache, palpitation, diaphoresis and mental fogginess.
The test is not indicated for evaluation of patients suspected to have primary adrenal insufficiency.
Once hypoglycemia is developed, providing intravenous 50% glucose solution or juice does not alter the result of the test.

Insulin Tolerance Test Procedure:

Establish hep-lock.

Draw baseline, timed samples after 30 min of patient rest for GH, cortisol, and glucose

Inject regular insulin IV in a single push as ordered by a physician and 10 cc saline flush following insulin.

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