Cortisol concentration is now measured on the Atellica (previous measurement was on the Immulite 2000). The interpretative comments have also been updated. Note that direct comparison between cortisol concentrations from different assays is not possible.
Standard ACTH (aqueous solution) stimulation protocol
- Take a 0h blood into a serum tube.
- Inject 5μg/kg Synacthen® IV.
- Take another blood sample 1h later into a serum tube.
- Label sample times clearly on the tubes.
- Tick Cortisol x 2 (code E02) l on submission form.
- If only submitting the 1h sample, tick Cortisol x 1 (code E01) but indicate in history that an ACTH stim test performed.
Vetnostics Pathology’s post-stimulation reference range and interpretation is based on this protocol. If using another protocol eg 1 ug/kg IV with testing exactly 60 minutes later (also adequate) or IM/SC protocols, the test details must be included. Synacthen can be stored frozen in appropriate aliquots for 6 months.
Depot ACTH (Synacthen® Depot) stimulation protocol
- Collect a basal (0 hour) blood sample into a serum tube.
- Inject 250ug of Synacthen® Depot IM.
- Collect a further blood sample into a serum tube 60 mins later.
- Label sample times clearly on the tube.
- Clearly indicate on the submission form that Depot Synacthen formulation was utilised as well as indicating dosage and blood sampling times.
- Tick Cortisol x 2 (code E02) l on submission form.
- If only submitting the 1h sample, tick Cortisol x 1 (code E01) but indicate in history that an ACTH stim test performed.
The Vetnostics Pathology reference intervals are not validated for this procedure. There is limited data available to assess the post-stim cortisol concentrations after depot Synacthen relative to the cortisol concentrations observed after aqueous Synacthen). From the limited literature available, testing at 60 minutes would appear to be the best approximation. Given that there is no longer a price advantage of depot Synacthen, we do not recommend this product routinely unless aqueous Synacthen is not available. There is no data that would validate freezing of any remaining depot Synacthen.
Following medical therapy for hyperadrenocorticism an ACTH stimulation test should be performed:
Trilostane
Perform the test 4-6 hours after administration of trilostane.
Mitotane
Perform the test 36-48 hours post administration of mitotane.
Comments
- Diagnostic testing for hyperadrenocorticism should not be performed in dogs that have severe non-adrenal illness as false positive test results may occur. In dogs with significant concurrent disease such as diabetic ketoacidosis or pancreatitis, adrenal function testing should be delayed until concurrent disease is either resolved or reasonably stable.
- All corticosteroids apart from dexamethasone will cross-react with the cortisol assay to some extent. To avoid cross-reaction interfering with the assay results, the following withholding times are recommended:
- Cortisone acetate 12h
- Prednisolone 24h
- Fludrocortisone 24h
- When assessing for hyperadrenocorticism in a dog that has been receiving corticosteroids, the appropriate withholding time must be observed and an ACTH stimulation test used in preference to a low dose dexamethasone suppression test.
