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A. Insulin-induced hypoglycemia test( insulin tolerance test (ITT) )

Insulin-induced hypoglycemia, are utilized to evaluate the response to stress, particularly when ACTH deficiency is suspected as the cause. This stress test also is used to establish a diagnosis of growth hormone deficiency.

測試方法

The ITT involves administration of regular insulin 0.1 U/kg IV (dose should be lower if hypopituitarism is likely) and collection of blood samples at 0, 30, 60, and 120 min for glucose, cortisol, and growth hormone (GH), if also assessing the GH axis. Oral or IV

glucose is administered after the patient has achieved symptomatic hypoglycemia (usually glucose <40 mg/dL). A normal response is defined as a cortisol >20 μg/dL and GH >5.1 μg/L. The ITT requires careful clinical monitoring and sequential measurements of glucose. It is contraindicated in patients with coronary disease, cerebrovascular disease, or seizure disorders, which has made the short cosyntropin test the commonly accepted first-line test

B. TRH stimulation test

A TRH stimulation test involves the intravenous administration of TRH (200 mcg) with

measurement of serum TSH at baseline and then 20 and 60 minutes after TRH

administration. The normal increment in TSH at 20 minutes is 5 to 30 mU/L, with a

subsequent decrease at 60 minutes. Classically, one would expect no serum TSH response

to TRH in patients with pituitary disease and a delayed response in patients with

hypothalamic disease. In fact, the response to TRH is highly variable in these

circumstances, limiting the utility of this test in distinguishing between pituitary and

hypothalamic disease as a cause of central hypothyroidism.

A TRH stimulation test may be useful in distinguishing nonthyroidal illness from

central hypothyroidism due to pituitary disease. Patients with nonthyroidal illness have

a blunted nocturnal rise in serum TSH concentrations, but they usually have a normal

serum TSH response to TRH.