Assessment of adrenocortical function

The synthetic polypeptide Synacthen (Tetracosactrin BP) has a structure identical to the N-terminal 24 amino acids of Adrenocorticotrophic Hormone (ACTH).

It has a short duration of action and permits a rapid and convenient screening test for the assessment of adrenocortical function by measuring cortisol response.

Measurement of additional adrenal steroids during the test (at the same time as the samples for cortisol - see below) may also be used to assess the steroid biosynthetic pathway.

Plasma 17-hydroxyprogesterone (17-OHP) measurements may assist in the diagnosis of non-salt-losing congenital adrenal hyperplasia.

If a defect in steroid biosynthesis is suspected, a random urine specimen for a full steroid profile taken before the Synacthen test may be helpful.

• Prednisolone and hydrocortisone both interfere with the measurement of cortisol.
• If the patient is already on hydrocortisone, ask the patient to omit their doses the evening before and on the morning of the test.
• The patient should continue taking the hydrocortisone immediately after the test whilst waiting for results.
• Patients taking Prednisolone should withhold the dose 24 hours before the Synacthen test.
  The patient does not need to fast.
• A cannula should be inserted at least 30 minutes before taking the baseline sample.

Drug(s) Given

Synacthen (Tetracosactrin BP) 250 micrograms.

For neonates and infants less than 7kg, give 36 micrograms/kg (rounded to the nearest 25 micrograms).

How Given

Intravenous bolus.

Timing of Administration

Give after basal sample has been taken.

A normal Cortisol response to synacthen at 60 min is greater than 430 nmol/L (Abbott Assay).

The exact values of cortisol cutoffs will be affected by the laboratory method used. Please consult your local laboratory.

Interpretation of plasma 17-OHP depends on age and clinical presentation.

Both adults and children usually have baseline 17-hydroxyprogesterone concentrations less than 6 nmol/l.

In late onset congenital adrenal hyperplasia, the baseline 17-hydroxyprogesterone may be either normal or high, but there is an exaggerated response (>30nmol/l) to Synacthen stimulation.