Dexamethasone Suppression Test

Screening test to confirm the diagnosis of Cushing’s disease/PPID (Horse)

Serum 2 x 0.5 ml or 3 x 0.5 ml

dog/cat

• First blood collection = baseline value
• Injection of dexamethasone i.m. or i.v. dog: 0,01 mg/kg bdw, cat: 0,1 mg/kg bdw
• Blood collection 4 hours post injection = 1st suppression value
• Blood collection 8 hours post injection = 2nd suppression value

• 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 = 1st suppression value – may be omitted
• 2nd suppression value after approx. 18 – 20 hours (at around 10 am – 1 pm) – obligatory
• Because of the circadian rhythm, the indicated times of the day should be observed.

Dog, cat, guinea pig, horse

dog/cat

• Normal: baseline value in reference range or slightly elevated (due to stress), 4 hours post injection reduction by 50% or to < 10 ng/ml and 8 hours post injection to < 10 ng/ml. .
• Cushing’s disease: baseline value in reference range or elevated and one or both suppression values > 10 ng/ml.
• The additional blood collection 4 hours p.i. gives information on whether Cushing’s disease is pituitary or adrenal.
• Pituitary: baseline value in reference range or elevated, 4-hour value reduced by 50% or to < 10 ng/ml and 8-hour value > 10 ng/ml.
• Adrenal tumour: baseline value in reference range or elevated, no adequate reaction to the administration of dexamethasone after 4 and 8 hours.

• PPID: one or both suppression values > 10 ng/ml
• Cave: In late summer/autumn, healthy horses, too, possibly suppress insufficiently.