Internal medicine: The ACTH stimulation test in diagnosing Addison's disease (hypoadrenocorticism)
The ACTH stimulation test for diagnosing Addison's disease (hypoadrenocorticism) in dogs and cats
The gold standard for diagnosing 
Addison's disease is the ACTH stimulation test.
Procedure:
1. Blood sample 1: Determination of basal cortisol level (serum 0.5 ml) and, if needed, further blood testing to determine endogenous ACTH (differentiation of atypical primary and secondary hypoadrenocorticism). Because ACTH is very unstable, consultation with the relevant laboratory is essential for correct sample handling!
2. Injection of synthetic ACTH (e.g. Synacthen®). Dogs: 5 µg ACTH/kg or 0.25 mg/animal IV or IM; Cats and dogs < 5 kg: 0.125 mg/animal IV or IM.
3. Blood sample 2: 1 hour post injection to determine stimulation level
Important: The patient should not have received glucocorticoid therapy (except in individual cases dexamethasone; see below) for at least 2 weeks beforehand. If, from a clinical point of view, an ACTH stimulation test is necessary despite previous administration of other glucocorticoids, consultation with the laboratory should also be made.
ACTH stimulation test and emergency treatment of a patient in addisonian crisis – a matter of management
A patient suspected of having an addisonian crisis represents an acute and life-threatening emergency requiring immediate intervention. However, if glucocorticoids are administered too hastily, an ACTH stimulation tests cannot be carried out for at least 2 weeks.
Therefore it is recommended that an ACTH stimulation test be done during emergency treatment before administering glucocorticoids. A corticoid preparation can then be administered after the test.
If, from a clinical point of view, immediate glucocorticoid treatment is essential, dexamethasone can be administered alone since little to no cross-reaction is to be expected. However, an ACTH stimulation test without prior administration of dexamethasone is preferred.
⇒ Did you know? ACTH stimulation tests are no longer part of standard diagnostics for Cushing´s disease (hyperadrenocorticism), because of the relatively high percentage of false negative results (failure to detect in afflicted animals). Instead, the low dose dexamethasone suppression test (LDDS test) is the method of choice.
Bibliography: Upon request
Author of the article:
Veterinarian met. ved. Julia Brüner