Which lab tests are performed to assess adrenocorticotropic hormone–releasing adenoma in hyperpituitarism?

Updated: Oct 24, 2016
  • Author: Alicia Diaz-Thomas, MD, MPH; Chief Editor: Robert P Hoffman, MD  more...
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See the list below:

  • Urinary steroid excretion: Urinary free cortisol (UFC) excretion is a direct measurement of cortisol not bound to plasma protein and is the most reliable and useful test for assessing cortisol secretion rate. Several 24-hour UFC measurements should be obtained. UFC values should be corrected for the child's body surface area. Daily UFC excretion in excess of 70 µg (over 24 consecutive hours) in the unstressed child is highly suggestive of hypercortisolism.

  • Plasma cortisol: Normal plasma cortisol values are highest from 6-8 am, declining during the day to less than 50-80% of morning values from 8 pm to midnight. Loss of this diurnal variation of plasma cortisol is typical of Cushing disease. Cortisol should be sampled at 30-minute intervals from 6-8 am and from 8 pm to midnight.

  • Dexamethasone suppression testing: A useful screening test for hypercortisolism is the inability of dexamethasone (0.3-0.5 mg/m2, maximum dose 1 mg) administered at 11 pm to suppress the subsequent 8-am plasma cortisol concentration to less than 5 µg /dL. The suppression of 24-hour UFC excretion by more than 50% with high-dose dexamethasone (120 µg /kg/d divided qid), but not by low-dose dexamethasone (30 µg /kg/d divided qid), suggests a primary hypothalamic-pituitary disorder. Lack of suppression to high-dose dexamethasone suggests an adrenal tumor or the ectopic secretion of ACTH.

  • Plasma ACTH: Elevated or high-normal values of plasma ACTH concentration in the presence of hypercortisolism suggest that the primary pathology is due to excess ACTH secretion of pituitary or nonpituitary origin. Consistently suppressed plasma ACTH concentrations suggest that the primary disorder lies in the adrenal glands.

  • Corticotropin-releasing hormone (CRH) stimulation testing: The ACTH and cortisol responses to CRH generally are flat in the ectopic ACTH syndrome and in hypercortisolism secondary to an adrenal tumor, whereas both remain intact in Cushing disease.

  • Inferior petrosal sinus sampling

    • Sampling for ACTH venous gradients during petrosal sinus catheterization in the areas of pituitary venous drainage can offer preoperative diagnosis of a corticotropinoma and lateralization of an ACTH-secreting microadenoma to the right or left hemisphere of the pituitary gland. A gradient in ACTH levels before and/or after CRH from either side of 2 or greater can localize a microadenoma in the pituitary in over 95% of the patients and can provide lateralization information in as many as 75% of cases. Thus, even very small tumors that are not visualized by MRI can be identified and excised surgically. Of note, this procedure should be performed only in large centers with extensive experience.

    • Because no healthy patient would undergo such an invasive procedure, the referring physician must advise families that appropriate reference ranges are not available. Thus, interpretation of these data are not straightforward. Indeed, these data often obscure the management and substantially inconvenience patients and their families with an interstate trip to an elite medical center.

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