corticotropin-releasing hormone (CRH) stimulation test

Indications: 1) reserved for differentiating difficult cases of Cushing's disease & ectopic ACTH-secreting tumors 2) used in conjunction with high-dose dexamethasone suppression test Specimen: -> plasma (heparin) for ACTH* 2) serum or plasma for cortisol* Procedure: 1) measure baseline plasma ACTH & cortisol 15 & 1 minute prior to administration of CRH 2) administer 1 ug/kg of ovine CRH IV at 0900-1200 hours 3) measure plasma ACTH & cortisol 5, 15, 30, 60 & 120 minutes after administration of CRH 4) specimens may also be drawn from inferior petrosal sinus (IPS) at 2, 5, 10 & 15 minutes after CRH administration & compared with values obtained from peripheral blood 5) procedure may be performed on an outpatient basis * sensitivity drops & specificity increases when only cortisol response is considered Reference interval: 1) 2-4 fold increase in mean baseline ACTH or cortisol 2) ratio of IPS/peripheral blood ACTH of > 3/1 Clinical significance: 1) pituitary Cushing's disease a) normal or exaggerated response to CRH b) IPS/peripheral blood ratio of > 3/1 2) ectopic ACTH-producing tumor a) no response to CRH b) IPS/peripheral blood ratio of < 3/1 Positive response to CRH stimulation or high dose dexamethasone suppression has 97% specificity for Cushing's disease. A lack of response to BOTH CRH stimulation & high dose dexamethasone suppression has 100% specificity for ectopic ACTH secretion, whereas either test alone has only 64-78% negative predictive value. ACTH concentrations peak 10-15 minutes after CRH injection. Peak values are higher in the morning than in the evening. Serum cortisol levels peak 30-60 minutes after ACTH injection. Peak values are NOT dependent upon time of day. Differential diagnosis: - Cushing's disease

Related

adrenocorticotropic hormone; corticotropin; adrenocorticotropin (ACTH) corticotropin-releasing factor; corticoliberin; CRF; corticotropin-releasing hormone (CRH) cortisol; hydrocortisone (Cortef, Solu-Cortef, Alphaderm, Cetacort, Cortenema, Nutracort) Cushing's syndrome; hypercortisolism; hyperadrenocorticism; pluriglandular syndrome

References

Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed., W.B. Saunders, 1995