Re: Sherry/ got info from Guelph re: Adjusted Listing for ACTH during seasonal rise

Suzanne and Pilgrim

Hi Sherry,

I called Guelph today.  The info I got from the Oct 20 testing was the following:  "The equine endogenous ACTH reference interval (2-10) reflects values obtained in mid to late summer, prior to the expected seasonal Fall) increase seen in this species.  Please refer to the AHL Lab Note #56-Equine PPID and EMS testing-for further details.  (I'm pretty sure that is just a generic statement in all reports.)

The following info is what I gleaned from Lab Note #56. I'm not sure if that is what you were requesting...

A "seasonal increase" in ACTH has been documented during the fall months, with median concentrations ~2 times the upper reference limit (although some healthy horses showed significantly higher values.  This seasonal increase has an impact in the interpretation of lab results.  Reference intervals at the AHL  (2-10 pmol/L) were developed outside the seasonal rise; thus, as an example, an ACTH result of 18 pmol/L could be unremarkable in the fall but would be interpreted as increased for the remainder of the year.  The seasonal rise in ACTH may also be exaggerated  in early PPID, increasing the sensitivity of the test, however seasonally adjusted reference intervals would be required for accurate interpretation.

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