Low
Dose Dexamethasone Suppression Test
Indications:
Diagnostic test for the
differentiation of normal dogs from those with
hyperadrenocorticism.
Notes:
In most situations, this is
regarded as the test of choice in the dog. The exceptions are:
- Testing for concomitant hyperadrenocorticism in
animals already known to have diabetes mellitus or renal disease.
In these cases, a significant incidence of false positive results
using the low dose suppression test has been reported.
- Testing for adrenocortical reserve in dogs on
therapy for hyperadrenocorticism
- Testing for iatrogenic hypercortisolism
In these situations, the ACTH
stimulation test is the test of choice.
Where there has been prolonged
(greater than 2 weeks) administration of oral prednisolone at
anti-inflammatory or higher doses, testing should be delayed for
at least 14 days after the withdrawal of therapy to allow
normalisation of the pituitary-adrenal axis.
Prior subcutaneous injection of
betamethasone or dexamethasone, delmadinone (Tardak) or
progestagens such as proligestone (Delvosterone) may also
significantly affect test results. Please contact the lab to
discuss the diagnostic approach to such cases.
Protocol:
N.B.
The dexamethasone supplied by
IDEXX Laboratories has a concentration of 4mg/ml, which is higher
than some veterinary products licensed for IV use. Using our
dexamathasone:
- The total injectable dose (ml) =
(bodyweight (kg) X 0.01) / 4
- Volumes for injection are small
for this test, and in some cases it can be helpful to make a 1:10
dilution of dexamethasone before administration.
- Collect 1-2 ml blood in plain/gel tube for basal
cortisol concentration.
- Immediately inject dexamethasone (0.01 mg/kg iv).
- Collect second blood sample for suppression test 3
hours post injection.
- Collect third blood sample for suppression test 8
hours post injection.
- Label tubes with name and time of sample. Submit
tubes and request form to the laboratory.
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