5 DAY SYNACTHEN STIMULATION TEST
INTRODUCTION
Tetracosactrin (Synacthen, Cortrosyn) is a synthetic preparation comprising the first 24 amino acids of ACTH. It stimulates the adrenal cortex to produce cortisol, failure to respond indicating impaired adrenocortical function. This test is indicated if the results of the short (30 minute) synacthen test are equivocal. It is usually performed on patients following total withdrawal of previous long term high dose glucocorticoid therapy, including topical preparations. It may also be used to differentiate primary adrenocortical insufficiency eg. Addison’s disease from insufficiency secondary to pituitary disease. This test is an in-patient procedure.
PRECAUTIONS
Please refer to the Trust’s phlebotomy procedure for sample collection precautions.
Neither pharmacological nor routine replacement doses of glucocorticoids should have been given for the previous 12 hours or during the test. Caution: Withdrawal of glucocorticoids may be dangerous. Dexamethasone (1mg), which does not interfere with the cortisol assay, should be given orally each day as a precaution against developing adrenocortical crisis.
Sodium and water retention may lead to oedema and heart failure. Allergic reactions to tetracosactrin are a possibility, but rarely occur.
PATIENT PREPARATION
The patient should remain at rest in bed prior to collection of the base-line sample. Smoking is not permitted.
PROTOCOL
1. |
Take basal venous blood sample (6ml SST tube – yellow top) |
2. |
1mg of Tetracosactrin Depot is administered intramuscularly daily at the same time for 5 days. |
3. |
Blood samples are collected 5 hours after each injection (6ml SST tube – yellow top) |
Label the samples with patient details and actual time taken. Send request form with full details of time of sample after last injection, the day of test and sample to Clinical Biochemistry Department as soon as possible.
INTERPRETATION
Normal Response:
The basal serum cortisol should be >140 nmol/l with a rise at 5 hours following the first injection to at least 1000 – 1800 nmol/l, being maintained throughout the test. No response at the end of 3 days confirms primary adrenocortical insufficiency. An impaired but increasing response indicates adrenocortical insufficiency secondary to pituitary disease or prolonged excessive glucocorticoid administration.
Reviewed by: Tony
Everitt, Consultant Biochemist
Last edited 07/08/08