Administration of supraphysiological dose of ACTH causes maximal release of cortisol by adrenal glands.
Uses
Alone
Diagnosis of hyperadrenocorticism .
Distinguishes spontaneous from iatrogenic hyperadrenocorticism .
Monitoring treatment of hyperadrenocorticism.
Diagnosis of hypoadrenocorticism .
In combination
In association with ACTH assay or high dose dexamethasone suppression test for differentiation of ADH and PDH.
Other points
Simple test to perform.
The only test that documents excessive production of glucocorticoids by the adrenal cortex - helpful to provide a baseline for monitoring mitotane therapy.
1-2 ml serum/heparinized plasma (3-5 ml whole blood) each sample.
For sample tube requirements see .
Sample collection technique
Fast animal for 12 h.
Collect 5 ml heparinized/clotted blood.
Standard protocol:
Inject synacthen (synthetic ACTH) :
<5 kg bodyweight: 0.125 mg.
>5 kg bodyweight: 0.25 mg.
Collect 5 ml clotted/heparinized blood 1 h later.
Separate serum/plasma.
Perform cortisol assay on both samples.
Alternative protocols also exist:
Depot ACTH: inject 1 mg IM, measure cortisol at 1 hr. NB Peak cortisol tends to be higher and more prolonged but [cortisol] at 1 hr similar to those for synacthen.
Low dose ACTH: inject synacthen <0.1 mg IV (doses of 0.1 µg/kg have been shown to be effective in stimulating cortisol), measure cortisol at 1 hr or 2 hr.
Quality control
Timing of test
Preferable to collect basal sample for [cortisol] between 9 and 10 am.
Sample storage
Once separated, plasma/serum can be frozen or stored for up to one week in fridge.
Test does not reliably differentiate ADH from PDH. Consider diagnosis of hyperadrenocorticism if signs compatible, even if normal ACTH response.
Animals under chronic stress, eg diabetes mellitus or pyometra, may develop adrenal hyperplasia abnormal ACTH response (becomes normal again after treatment of underlying disease).
Dunn K J, Herrtage M E & Dunn J K (1995) Use of ACTH stimulation tests to monitor the treatment of canine hyperadrenocorticism.Vet Rec137 , 161-165 PubMed.
Kaplan A J, Peterson M E & Kemppainen R J (1995) Effects of disease on the results of diagnostic tests for the use in detecting hyperadrenocorticism in dogs.JAVMA207 , 445-451 PubMed.
Vetstream contributor(s)
Dr David Bruyette DVM DipACVIM , VCA West Los Angeles, 1818 South Sepulveda Boulevard, Los Angeles, CA 90025, USA.
Consider diagnosis of hyperadrenocorticism if signs compatible, even if normal ACTH response.
abnormal ACTH response (becomes normal again after treatment of underlying disease).