Indication

1. Diagnosis of adrenal insufficiency.
2. With basal ACTH measurements, useful in differentiating primary from secondary insufficiency.
3. To screen for secondary adrenal insufficiency – not suitable for patients within 14 days of pituitary surgery or any other possible acute presentation of hypopituitarism eg pituitary apoplexy.
4. In congenital adrenal hyperplasia – see separate protocol.

Cautions

• If adrenal insufficiency is strongly suspected clinically, treatment with hydrocortisone should not be delayed in order to perform the test. In such circumstances the test can be performed subsequently following withdrawal of hydrocortisone for 12 hours.
• Anaphylactic reactions to tetracosactide (Synacthen®) can occur rarely. The test must be performed in a location where resuscitation facilities are available.
• In patients receiving exogenous steroids there is likely to be adrenal suppression and the interpretation of the results will be difficult.
•  Patients on oestrogen (HRT or combined oral contraceptive pill) should discontinue this 6 weeks prior to the test (to eliminate the effect of oestrogen on increasing cortisol binding globulin).

Patient preparation

1. In patients receiving prednisolone or hydrocortisone, the test must be performed at least 24 and 12 hours respectively after the last dose, as there is cross reactivity in the cortisol assay.
2. Fasting is not required.

Procedure

If possible the test should be started between 08:00 and 10:00 hours.
Remember to label all samples clearly with patient’s full name, date of birth and time of sample.

1. Insert IV cannula*, flush with 2mL of 0.9% sodium chloride and wait 15 minutes.
2. Take and discard 2mL of blood from the cannula (to avoid contamination of the sample with sodium chloride), then take blood samples for cortisol (gel tube) and, if required, ACTH (EDTA tube).
   Send ACTH sample to Biochemistry as soon as it is taken.
   Phone Biochemistry to let laboratory know ACTH sample is coming.
   ACTH is not necessary if assessing adrenal suppression from long term steroid use.
3. Inject 250micrograms tetracosactide (Synacthen^®) IV* and flush with 2mL of 0.9% sodium chloride.
4. At 30 minutes take second blood sample (procedure as above) for cortisol.
   *Note: Alternatively, 250micrograms of Synacthen^® can be administered IM and blood samples taken by simple venepuncture to avoid the need for cannulation.

Interpretation

• Normal response: 30 minute cortisol > 550 nanomol/L.
• ACTH will only be sent for analysis in the event of an abnormal response.
• Discuss indeterminate results with referring clinician.