September 24, 2017
Short Synacthen Test for hypoaldosteronism Minimize

Short Synacthen test for hypoaldosteronism

Indication

This is performed for the investigation of adrenal insufficiency as a cause of isolated hypo aldosteronism.

Contraindication

The Synacthen test gives unreliable results within 2 weeks of pituitary surgery.

Principle

Aldosterone is largely regulated by angiotensin (following degradation of angiotensiogen by plasma renin). However, aldosterone also responds to adrenal stimulation by ACTH. This test is based on this regulation and uses synthetic ACTH (tetracosactide; Synacthen ®).

Side effects

There are rare reports of hypersensitivity reactions to ‘Synacthen’ particularly in children with history of allergic disorders.

Preparation

There are no dietary restrictions for this test. This test should be performed in the morning after 60 min bed rest.

Requirements

  • 2 serum tubes and one plasma tube (for renin)
  • 250 microgram Synacthen (1 vial)
  • the dose for children is 36 microgram/kg body weight up to a maximum of 250 micrograms

Procedure

0900

take 3 mL blood for cortisol and aldosterone
take 2 mL for plasma renin
inject Synacthen iv or im

0930

take 3 mL blood for cortisol and aldosterone

Interpretation

  1. Adrenal glucocorticoid insufficiency is excluded by an incremental rise in cortisol of > 200nmol/L and a 30 min value > 600 nmol/L.
  2. Failure of aldosterone concentrations to increase by at least 150 pmol/L from baseline 30 min after administration of Synacthen is indicative of inadequate zona glomerulosa function.
  3. A diagnosis of isolated primary hypoaldosteronism rests upon raised PRA, low plasma aldosterone concentration, inadequate response of aldosterone to ACTH associated with a normal cortisol response.

Sensitivity and Specificity

 

References

  • Clarke PMS, Neylon I, Raggatt PR, Sheppard MC, Stewart PM. Defining the normal cortisol response to the short Synacthen test: implications for the investigation of hypothalamo-pituitary disorders. Clin Endocrinol (Oxf) 1998;49:287-292.
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