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insulin tolerance test (ITT)
Indications:
- evaluation of growth hormone deficiency
- evaluation of ACTH deficiency
Contraindications:
- caution:
a) fatal hypoglycemia may occur
b) a physician must be present during testing Normal values:
- serum glucose
- baseline & 4 time points
- falls to 50% of fasting level with 20-30 minutes
- returns to baseline within 90-120 minutes
- serum growth hormone (for growth hormone deficiency)
- baseline & 4 time points
- serum cortisol (for hypopituitarism, ACTH deficiency)
- baseline & 4 time points
Clinical significance:
- the insulin tolerance test is the gold standard for assessment of the hypothalamic-pituitary-adrenal axis, but is rarely needed
- it offers no advantage over the cosyntropin-stimulation test except in the first few days after acute ACTH deprivation
- increased tolerance
- hypothyroidism
- acromegaly
- Cushing's syndrome
- diabetes mellitus
- decreased tolerance
- pancreatic islet cell tumor
- adrenal insufficiency secondary to hypopituitarism
- von Gierke disease
- starvation
- growth hormone deficiency
Procedure:
1) regular insulin is injected IV 0.1 units/kg
2) serum glucose & cortisol levels are drawn at 0, 30, 60 & 90 minutes
Interpretation:
1) symptomatic hypoglycemia (< 40 mg/dL) is suggestive of adrenal insufficiency
2) a peak cortisol level of > 20 ug/dL is normal
Adverse effects:
1) fatal hypoglycemia may occur
2) a physician must be present during testing
3) 50% glucose for IV injection should be available at the bedside
Related
Addison's disease (primary adrenal failure)
adrenocorticotropic hormone; corticotropin; adrenocorticotropin (ACTH)
aldosterone (Electrocortin, Aldocortin)
cortisol; hydrocortisone (Cortef, Solu-Cortef, Alphaderm, Cetacort, Cortenema, Nutracort)
cosyntropin (ACTH, Cortrosyn) stimulation test (delta cortisol test)
glucose (dextrose, D-glucose)
secondary adrenal insufficiency (SAI)
General
provocative clinical test
special chemistry test
References
- Saunders Manual of Medical Practice, Rakel (ed), WB Saunders,
Philadelphia, 1996, pg 654
- Interpretation of Diagnostic tests, 8th edition, Wallach J,
Lippincott, Williams & Wilkens, Philadelphia, 2007