Corticotropin Releasing Hormone Stimulation Test

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Contents 1 Indications 2 Reference-interval 3 Clinical-significance 4 Specimen 5 Procedure 6 Differential-diagnosis 7 More General Terms 8 Additional Terms 9 References

Indications

• reserved for differentiating difficult cases of Cushing's disease & ectopic ACTH-secreting tumors
• used in conjunction with high-dose dexamethasone suppression test

Reference-interval

• 2-4 fold increase in mean baseline ACTH or cortisol
• ratio of IPS/ peripheral blood ACTH of > 3/1

Clinical-significance

• pituitary Cushing's disease

• normal or exaggerated response to CRH
• IPS/ peripheral blood ratio of > 3/1

• ectopic ACTH-producing tumor

• no response to CRH
• 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.

Specimen

• plasma ( heparin) for ACTH*
• serum or plasma for cortisol*

Procedure

• measure baseline plasma ACTH & cortisol 15 & 1 minute prior to administration of CRH
• administer 1 ug/kg of ovine CRH IV at 0900-1200 hours
• measure plasma ACTH & cortisol 5, 15, 30, 60 & 120 minutes after administration of CRH
• 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
• procedure may be performed on an outpatient basis
  

• * sensitivity drops & specificity increases when only cortisol response is considered

Differential-diagnosis

• Cushing's disease

More General Terms

• provocative clinical test

Additional Terms

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

References

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

corticotropin-releasing hormone (CRH) stimulation test