The clinical pathology section at the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) is excited to announce an improved profile for dexamethasone suppression testing in horses, the Cortisol –Dexamethasone Suppression Profile – Equine. This new test offering provides the same clinical information, however, it requires fewer specimens and can be performed at a decreased cost.
The Dexamethasone Suppression Profile is a standard, widely used testing protocol to evaluate horses with suspected Pituitary Pars Intermedia Dysfunction (PPID). This testing protocol involves collecting a baseline cortisol sample, administering Dexamethasone at 40 µg/kg IM, and collecting one or multiple post-Dexamethasone cortisol samples. In normal horses, cortisol should suppress to <1.00 µg /dL in the 15-hour to 19-hour interval following the administration of Dexamethasone.
TVMDL’s previous profile (Cortisol – Low Dose Dexamethasone Suppression Profile – Equine), required a baseline cortisol sample and two post-Dexamethasone cortisol samples: collected at 15- and 19-hours. Collecting two post samples can be difficult for the veterinarian, animal owner, and patient.
TVMDL recently evaluated cortisol concentrations in horses undergoing Dexamethasone suppression testing where samples were collected at 15-hours and 19-hours after administration of Dexamethasone. In 92% of horses, the 15-hour and 19-hour cortisol concentrations were identical in terms of clinical interpretation (appropriate or inappropriate suppression, when using a strict 1.00 ug/dL cut-off value). In the remaining cases, the difference between the 15-hour and 19-hour cortisol concentrations was mild and would be considered equivocal. In other words, the two different values would not have confidently resulted in a different diagnosis. Given these findings, the evaluation of one sample collected between 15-hours and 19-hours after administration of Dexamethasone is likely sufficient. Dexamethasone Suppression Profile results should always be interpreted in conjunction with the clinical history of the patient due to the possibility of false negatives and false positives.
For further information on the Dexamethasone Suppression Profile for horses, please visit the TVMDL website or TVMDL Mobile app. Additional test offerings for PPID (endogenous ACTH) are also available on the TVMDL website and mobile app.