Short-Term Effects of Temperature and Thyrotropin-Releasing Hormone Stimulation on Adrenocorticotropin Stability in Horses.
Authors: Hinrichsen Sophia L, Yuen Ka Y, Dryburgh Elizabeth L, Bertin François-René, Stewart Allison J
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Pituitary pars intermedia dysfunction (PPID) diagnosis relies on ACTH measurement, either at baseline or following thyrotropin-releasing hormone (TRH) stimulation, yet ACTH's notorious instability poses practical challenges for laboratories and practitioners alike. Researchers exposed whole blood samples from 15 horses (8 with confirmed PPID, 7 without) to five different temperatures ranging from 4°C to 70°C over one hour, comparing basal ACTH stability against post-TRH stimulation samples to determine whether temperature exposure and hormonal status affected immunoreactive ACTH concentrations. Temperature significantly influenced ACTH readings (p = 0.003), with non-PPID horses showing greater susceptibility than their PPID-positive counterparts; however, samples stored at 20°C showed minimal drift of only 5% in PPID horses and 12% in non-PPID horses after 60 minutes, whilst higher temperatures produced unpredictable—occasionally clinically meaningful—variations. TRH stimulation itself did not meaningfully alter ACTH stability. Whilst maintaining samples at 4°C remains the gold standard, occasional deviations up to 40°C for brief periods appear unlikely to invalidate results, though warmer temperatures introduce cumulative diagnostic risk and should be avoided when possible, particularly in borderline cases or non-PPID horses where wider fluctuations become more problematic.
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Practical Takeaways
- •Keep ACTH samples at 4°C for optimal results, but samples accidentally left at room temperature (20°C) or warmer up to 40°C are still usable within 1 hour, minimizing false PPID diagnoses from sample degradation
- •Be aware that temperature-related ACTH changes are less predictable in non-PPID horses, so always prioritize proper sample handling to avoid misdiagnosis
- •TRH stimulation does not worsen ACTH instability, so post-stimulation samples can be handled using the same temperature guidelines as basal samples
Key Findings
- •Temperature significantly affected immunoreactive ACTH stability (p = 0.003), with greater effects in PPID-negative horses (p = 0.01)
- •At 20°C, mean ACTH concentrations changed minimally by 5% in PPID horses and 12% in non-PPID horses after 1 hour
- •Samples stored at temperatures up to 40°C for 1 hour can provide valid results, though this increases risk of altered ACTH concentrations affecting PPID diagnosis
- •TRH stimulation had no significant effect on ACTH stability across different temperatures