July 23, 2017
CRH Test Minimize

Corticotrophin releasing Hormone (CRH) Test

Indication

Human or ovine CRH is given to test for i) pituitary ACTH deficiency ii) to differetiate between pituitary from ectopic source of ACTH in Cushings and iii) to investigate pseudo-Cushings (see interpretation). THis test may be performed at the time of inferior petrosal sinus sampling where it may help in lateralising the source of pituitary ACTH.

Contra-indication

None

Principle

CRH is normally released by the hypothalamus to stimulate ACTH release by the anterior pituitary.

Preparation

The patient should have fasted for at least 4 hours

Requirements
  1. 6 plain tubes for cortisol and 6 EDTA tubes for ACTH
  2. ice bucket with water ice to keep samples cold
  3. CRH - dose 1µg/kg boy weight (max dose 100µg)

Procedure

 time -15 min take 3mL blood for ACTH and cortisol 
 Time 0 min  give CRH over 60 seconds
 time 5 min  take 3mL blood for ACTH and cortisol
 time 15 min  take 3mL blood for ACTH and cortisol
 time 30 min  take 3mL blood for ACTH and cortisol
 time 45 min  take 3mL blood for ACTH and cortisol
 time 60 min  take 3mL blood for ACTH and cortisol

Interpretation

  • Responses to CRH are quite variable both within and between individuals. In normal individuals plasma ACTH rises by 400% (mean) at 10-30 min post-CRH. and serum cortisol by 250% (mean) with a peak at 30-60 min post-CRH.
  • There are different respones at different time of day duer to higher basal values of ACTH and cortisol early in the morning.
  • Patients with pituitary Cushings show an increase in ACTH of at least 35-50% to ovine CRH
  • Approximately 8% patients with Cushing's Disease  do not have an appreciable ACTH or cortisol response to CRH. These patients may require inferior petrosal sinus sampling.
  • Inferior petrosal sinus sampling is probably the best test for distinguishing Cushing's Disease from ectopic ACTH syndrome.
  • The have been reports of patients with ectopic ACTH production responding to CRH.
  • Imiprimanine may reduce ACTH response

References

  •   Nieman LK, Lacroix A, Martin KA. Corticotrophin-releasing hormone stimulation test. UpToDate April 2012

J.H.Barth 14 June 2012

  

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