In the 04 August 2011 Prascend webinar, Andy Durham of Liphook Equine Hospital said that horses with PPID have a much greater autumnal increase in ACTH than normal horses, therefore this is the BEST time to test for PPID as the difference between horses with PPID and normal horses is magnified, as long as a seasonally adjusted reference range is used. Liphook tested ACTH from 156 normal horses every month for a year and plotted the upper limit reference interval. August, September and October had a mean upper limit of 47 pg/ml with September having the highest at over 50 pg/ml. The mean upper limit for the rest of the year was 29 pg/ml with January, March, July, November and December all having mean upper limits over 30 pg/ml.
See Liphook Equine Hospital and Laboratory - PPID for more information.
Cathy McGowan echoed this in her 11 August 2011 Prascend webinar - "if you test ACTH in the autumn with seasonally adjusted ACTH reference ranges, you have an increased chance of picking up PPID cases", and Cathy suggested that if an ACTH test has not previously been diagnostic, it could be worth retesting ACTH in the autumn.
See Liphook Equine Hospital and Laboratory - PPID for more information.
Cathy McGowan echoed this in her 11 August 2011 Prascend webinar - "if you test ACTH in the autumn with seasonally adjusted ACTH reference ranges, you have an increased chance of picking up PPID cases", and Cathy suggested that if an ACTH test has not previously been diagnostic, it could be worth retesting ACTH in the autumn.