- To assess ACTH and cortisol reserve.
- To assess GH reserve in children with definite growth retardation and a subnormal growth hormone stimulation test.
- To differentiate Cushing’s syndrome from depression.
- To assess GH response in adults.
Ischemic heart disease,
9am Serum cortisol <3.625 µg/dL
- Overnight fasting is required. ECG must be normal and the patient’s weight known.
- In peri-pubertal children (bone age > 10 years) priming is needed.
- Calculate Actrapid Insulin dose,Oral oestrogens to be discontinued 6 weeks before the test.
- 20% dextrose must be available for immediate administration.
- Glucometer,6 grey top Vacutainers, 6 red or yellow top Vacutainers are required.
Sweating, palpitations, loss of consciousness and rarely convulsions.
- Insert I.V cannula, take baseline blood samples and then inject insulin I.V
- Take samples for GH, cortisol and glucose at 0, 30, 60, 90, and 120 minutes, flushing the cannula with saline between samples.
- Check glucose on glucometer every time a specimen is taken. At 30 minutes, if patient is not hypoglycemic, repeat the insulin dose. (This means prolonging sampling by 30 min).
- Adequate hypoglycemia is defined as glucose £40 mg/dl with symptoms.
- Reverse hypoglycaemia with simple oral treatment or I.V. 20% dextrose, or 1 mg I.M. glucagon and continue sampling.
- Once test completed, give supervised meal and ensure glucose is normal before discharging.
IMPORTANT NOTE ON ITT CORTISOL INTERPRETATION
The cortisol response to stress and to an ITT is highly variable. ITT is used as a surrogate for stress, assumes that if patients cannot produce atleast 13.59 µg/dL of cortisol during the ITT, that they might suffer an Addisonian crisis at times of stress. It also assumes that patients who produce >18.2 µg/dL cortisol during an ITT are very unlikely to have an Addisonian crisis at times of stress, and thus do not need regular cortisol replacement.
- The test cannot be interpreted unless hypoglycaemia <40 mg/dl is achieved.
- Adequate cortisol response is defined as a rise of greater than 5.43 µg/dL to 18.2 µg/dL or above.
- In Cushing’s syndrome there will be a rise of <5.07 µg/dL above the fluctuations of basal levels of cortisol.
- As per European and Endo Society guidelines, severe GHD is defined as GH <3mcg/L and partial as GH<5mcg/L.
- In children a rise to >10 mcg/L (>39 mU/L) is considered normal. Appropriate priming is very important if they are peri-pubertal.
- By consensus, children should have two different stimulatory tests before assigning a diagnosis of isolated GH deficiency (e.g. insulin, glucagon or GHRH-arginine tests) unless IGF-1 is decreased in which case one test may be considered adequate.
SENSITIVITY AND SPECIFICITY
If there is adequate hypoglycaemia and the patient is not hypothyroid then cortisol response is a good test of ACTH/adrenal reserve.
5-15% of normal people will show a suboptimal response as defined by these two criteria.
à20% of patients with Cushing’s syndrome will show a rise greater than 140 µg/dL but a rise of less than this is rare in depression or alcoholic pseudo-Cushing’s.
àGH responses are reduced in 20% of normal children and some small children whose peak GH is 3-6mcg/L(10-20mU/l) may benefit from GH replacement.