ACTH Stimulation Test
Indications:
Diagnostic test for the differentiation of normal dogs from those
with hypo- or hyperadrenocorticism.
Test of choice for the assessment of:
i) adrenocortical reserve in dogs on treatment for
hyperadrenocorticism.
ii) the presence of concurrent hyperadrenocorticism in diabetic
dogs.
iii) diagnosis of suspected hypercortisolism in dogs that have a
history of steroid therapy.
Notes:
ACTH is not licensed for use in the dog. ACTH stimulation testing
in many published surveys has a slightly lower sensitivity than the
low dose dexamethasone suppression test which, except in the
circumstances outlined above, would be our recommended screening test
for hyperadrenocorticism.
Results of ACTH stimulation can be affected by prior glucocorticoid
administration, stress, anticonvulsant therapy and chronic disease. As
a result, final interpretation of the results must be made in the
context of the history and clinical findings. ACTH stimulation tests,
in common with other endocrine tests, can be associated with
occasional false positive and negative results.
Where there has been prolonged (greater than 2 weeks)
administration of glucocorticoids at anti-inflammatory or higher
doses, ACTH testing should be delayed for at least 14 days after the
withdrawal of therapy to allow normalisation of the pituitary-adrenal
axis. Chronic anticonvulsant medication can be associated with
abnormal cortisol concentrations and test results must be interpreted
with caution in such cases.
Injectable drugs, including betamethasone, dexamethasone,
depomedrone, delmadinone (Tardak) and proligestone, may all affect
ACTH test results for variable periods of time. Please contact the
laboratory to discuss the diagnostic approach to cases where these
drugs have been administered.
As the results of iatrogenic hypercortisolism and spontaneous
hypoadrenocorticism can be similar on ACTH testing, a history of prior
drug therapy is helpful in interpreting the test.
Protocol:
To minimise diurnal variation, it is preferable to commence this
test as early as possible in the morning.
- Collect 1-2 ml blood in plain/gel tube.
- Administer 0.25 mg (250 µg) Synacthen (intravenously).
- Collect 1-2 ml blood sample at 120 minutes post-injection.
- Label tubes with name and time of sample.
- Submit tubes and request form to the laboratory.
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