Insulin Tolerance Test

From Anvita Health Wiki

Contents 1 Indications 2 Contraindications 3 Adverse-effects 4 Clinical-significance 5 Procedure 6 Interpretation 7 More General Terms 8 Additional Terms 9 References

Indications

• evaluation of growth hormone deficiency
• evaluation of ACTH deficiency

Contraindications

• caution:

• fatal hypoglycemia may occur
• 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

Adverse-effects

• fatal hypoglycemia may occur
• a physician must be present during testing
• 50% glucose for IV injection should be available at the bedside

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

• regular insulin is injected IV 0.1 units/kg
• serum glucose & cortisol levels are drawn at 0, 30, 60 & 90 minutes

Interpretation

• symptomatic hypoglycemia (< 40 mg/dL) is suggestive of adrenal insufficiency
• a peak cortisol level of > 20 ug/dL is normal

More General Terms

• provocative clinical test
• special chemistry test

Additional Terms

• Addison's disease (primary adrenal failure)
• adrenocorticotropic hormone; corticotropin; adrenocorticotropin (ACTH)
• aldosterone (Electrocortin, Aldocortin)
• cortisol; hydrocortisone (Cortef, Solu-Cortef, Alphaderm, Cetacort, Cortenema, Hytone, Nutracort, Westcort)
• cosyntropin (ACTH, Cortrosyn) stimulation test (delta cortisol test)
• glucose (dextrose, D-glucose)
• secondary adrenal insufficiency (SAI); central adrenal insufficiency

References

1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 654
2. Interpretation of Diagnostic tests, 8th edition, Wallach J, Lippincott, Williams & Wilkens, Philadelphia, 2007

insulin tolerance test (ITT)