ACTH Stimulation Test

• Diagnosis of hypoadrenocorticism (Addison’s disease)
• Clarification of iatrogenic Cushing’s syndrome
• Suspected Cushing’s syndrome
• Horse: clarification of hypoadrenocorticism (Addison’s disease)

Serum 2 x 0.5 ml

• First blood collection = baseline value
• Dog: injection of 5 μg ACTH/kg as Cosacthen® i.v./(i.m.)
• Cat: injection of 5 μg/kg Cosacthen® i.v./(i.m.)
• Second blood collection (= stimulation value) in dog, cats one hour post injection
• Guinea pig: baseline value cortisol, 2 IU ACTH/kg, i.v./i.m., second sample collection after 4 hours
• Horse: injection of 100 IU ACTH i.v.
• Second blood collection 2 hours post ACTH administration = stimulation value in horses

Cortisol

Chemiluminescence assay (CLIA)

Dog, cat, horse, guinea pig, others on request

Reporting of results on the day the sample is received (Mon–Sat)

• To assess cortisol concentration, previous glucocorticoid treatment should be ruled out (except when clarifying iatrogenic Cushing’s syndrome).
• Clinical issue diagnosis of hypoadrenocorticism (Addison’s disease): Dogs with hypoadrenocorticism typically have concentrations in the lower reference range or below. Stimulation typically results in no or only a slight increase in cortisol concentrations. The intake of steroids can produce similar results.
• Clinical issue diagnosis of Cushing’s syndrome: Cushing’s syndrome may be considered if the clinical signs are consistent and stimulation values are elevated. In dogs, the ACTH stimulation test is considered more specific but less sensitive than the lowdose dexamethasone suppression test for diagnosing Cushing’s syndrome. False negative results are common, especially if Cushing’s syndrome is caused by an adrenal tumour.
• Other underlying conditions (e.g. diabetes mellitus) can also lead to elevated stimulation values.
• Clinical issue therapy monitoring for Cushing’s syndrome: When treating with trilostane (Vetoryl®), the target stimulation value is between 20 ng/ml and 50 ng/ml. For evaluating this treatment, “Trilostane Therapy Control” (see Endocrinology) is also available.
• Horse: In healthy animals, the cortisol level increases by approximately 80%; horses with hypoadrenocorticism (Addison’s disease) show very low baseline values which do not or only slightly increase after stimulation.
• Guinea pig: for therapy monitoring of Cushing’s disease; at the time of diagnosis, it is not possible to differentiate between pituitary and adrenal Cushing’s syndrome; there are no reference values available.

In guinea pigs, an ACTH stimulation test can also be performed using saliva (servie ID 1329 Salivary Cortisol Stimulation Test). Sample tubes are provided; saliva samples are analysed using ELISA detection method.