Care is required in looking after blood samples before they are tested for evidence of equine Cushing’s disease to ensure satisfactory results, Australian researchers caution.
Leaving samples in a hot car, for example, could affect levels of the hormone which is to be measured, they report.
Equine Cushing’s disease, more formally known as pituitary pars intermedia dysfunction (PPID), affects about 20% of older horses. The condition is associated with hair-coat changes, muscle loss, and a higher risk of developing an infection or laminitis.
Elevated plasma levels of the adrenocorticotropic hormone (ACTH) is used to diagnose PPID. However, the hormone is not stable in blood samples. Ideally, samples should be kept at 4 degrees Celsius until analysis.
However, in traditional equine veterinary practice, blood samples can be left at room temperature – 20 or 30 degrees Celsius – or inadvertently left in a vehicle without refrigeration where they might be exposed to temperatures of up to 70 degrees in hot climates.
Researchers in a University of Queensland study set out to evaluate the effects of temperature on ACTH concentrations.
Sophia Hinrichsen and her fellow researchers experimentally subjected blood samples from 15 horses, aged 11 to 27, with and without PPID, to temperatures of 4, 20, 30, and 70 degrees for one hour before laboratory measurement.
Eight of the horses were confirmed beforehand to have PPID, while the other seven did not have the condition.
The authors, writing in the journal Animals, found that the stability of ACTH was affected by short-term exposure to high temperatures in horses with and without PPID.
The effects of the high temperatures proved to be unpredictable, resulting in both higher and lower measured concentrations when compared to levels in the reference samples kept at 4 degrees.
“Our results suggest that samples should be kept at 4 degrees Celsius to reflect the true ACTH concentration,” the study team concluded.
They said exposure to temperatures of up to 40 degrees for one hour can still provide an appropriate assessment of pituitary function in most cases if analyzed within an hour, but even so the ACTH concentration changed by 12% in healthy horses and 5% in horses with PPID.
About 40% of samples exposed to 70 degrees were unmeasurable, they found.
The study team comprised Hinrichsen, Ka Yuen, François-René Bertin and Allison Stewart, all with the University of Queensland; and Elizabeth Dryburgh, with Boehringer Ingelheim Animal Health Australia.
Hinrichsen, S.L.; Yuen, K.Y.; Dryburgh, E.L.; Bertin, F.-R.; Stewart, A.J. Short-Term Effects of Temperature and Thyrotropin-Releasing Hormone Stimulation on Adrenocorticotropin Stability in Horses. Animals 2022, 12, 324. https://doi.org/10.3390/ani12030324