| Diagnosis | Testing for Cushing’s syndrome / Suspected PPID (Cushing’s disease) |
| Material | Serum 2x 0.5 ml or 3x 0.5 ml (see also remark) |
| Execution | Dog/cat/Guinea pig
- First blood collection = baseline value
- Administration of dexamethasone:
Dog i.v. (or i.m.): 0.01 mg/kg bdw
Cat i.v. (or i.m.): 0.1 mg/kg bdw
Guinea pig i.m. or i.v.: 0.1 mg/kg bdw - Blood collection 4 hours post injection = 1st suppression value
- Blood collection 8 hours post injection = 2nd suppression value
Horse (Overnight Dexamethasone Suppression Test)- First blood collection = baseline value (blood sampling at around 4–6 pm)
- Injection of 2 mg/50 kg bdw of dexamethasone i.v.
- Blood sampling approx. 15 hours after administration of dexamethasone (at around 8–10 am) = 1st suppression value – may be omitted
- 2nd suppression value after approx. 18–20 hours (at around 10 am–1 pm) – the decisive value
- Because of the circadian rhythm, the indicated times of the day should be observed.
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| Parameter | Cortisol |
| Method | Chemiluminescence assay (CLIA) |
| Species list | Dog, cat, guinea pig, horse |
| Duration | Reporting of results on the day the sample is received (Mon–Sat) |
| Assessment | Dog/cat:
- Both suppression values < 10 ng/ml: Cushing’s syndrome unlikely
- One suppression value < 10 ng/ml: Cushing’s syndrome questionable
- Insufficient suppression: A lack of suppression may indicate the presence of Cushing’s syndrome if the clinical picture is appropriate. Insufficient suppression is also seen in other diseases.
Guinea pig:- Evaluation: adequate suppression and interpretation as in dogs, reference values not available
- For testing using saliva, see the Saliva Cortisol Suppression Test
Horse:- PPID: one or both suppression values > 10 ng/ml
- Cave: In late summer/autumn, healthy horses, too, possibly suppress insufficiently.
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| Remark | - The test with examination of 2 suppression values (3 serum samples) can be found on the online submission forms and in the practice programmes under service ID 1142.
- Can be performed as an alternative to the TRH Stimulation Test.
- PPID (formerly known as Cushing’s disease) in horses is caused by “pituitary adenoma” (hyperplasia of the pars intermedia). The hyperplastic cells have no cortisol receptors, that is why in PPID, the exogenous administration of dexamethasone does not suppress the endogenous secretion of corticoids as it does in healthy horses.
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