Dexamethasone Suppression Test

LABOKLIN Service ID: 142

Diagnosis

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

Material

Serum 2 x 0.5 ml or 3 x 0.5 ml

Execution

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

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 = 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.

Species list

Dog, cat, horse

Assessment

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.

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