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Discussion on Variation in ACTH and dex suppression test with season
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Moderator:
DrO
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Posted on Thursday, May 19, 2005 - 9:14 am:
We have reported on this before but it bears repeating that the results of testing for Cushingnoid Disease in horses is very dependent on season. False positive DST tests occur quite commonly in the fall. That is about 1/4 of the horses that have normal DST's in the winter and spring will have "abnormal" DST's suggestive of Equine Cushingnoid Disease in the fall.
J Vet Intern Med. 2005 Mar-Apr;19(2):217-22.
Variation in plasma adrenocorticotropic hormone concentration and dexamethasone suppression test results with season, age, and sex in healthy ponies and horses.
Donaldson MT, McDonnell SM, Schanbacher BJ, Lamb SV, McFarlane D, Beech J.
Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA, USA. mtd@vet.upenn.edu
The purpose of this study was to evaluate the variation in plasma adrenocorticotropic hormone (ACTH) concentration and dexamethasone suppression test (DST) results with season, age, and sex in healthy, pony mares (n=15) and pony stallions (n=14) living under semiferal conditions and horse mares (n=10) living at pasture. Plasma ACTH concentrations were measured in September 2002, and in January, May, and September 2003. DSTs were performed in January and September 2003. Plasma ACTH concentrations in September 2002 and September 2003 were similar and were significantly greater than in January and May (P <.001).> .05). Seasonal changes in plasma ACTH concentration and DST results should be considered when interpreting endocrine test results.
The results of this research suggest strongly that horses with abnormal results in late summer and early fall should be retested in the winter to confirm results, for our recommendations on diagnosis see the article, Cushing's SynDrOme and Pituitary Tumors.
DrO
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