The effects of sample handling and N-phenylmaleimide on concentration of adrenocorticotrophic hormone in equine plasma.
Authors: Rendle D I, Litchfield E, Gough S, Cowling A, Hughes K J
Journal: Equine veterinary journal
Summary
# Editorial Summary: ACTH Stability in Equine Plasma Rapid degradation of adrenocorticotrophic hormone (ACTH) has long been cited as a practical limitation in diagnosing equine pituitary pars intermedia dysfunction (PPID), prompting Rendle and colleagues to systematically investigate how sample handling affects ACTH measurement stability. Blood from eight healthy horses and eight PPID-affected animals was processed under three protocols (immediate centrifugation, immediate centrifugation with protease inhibitor, and gravity separation with inhibitor), then analysed at 4, 8, 24 and 48 hours post-collection using chemiluminescent assay. Whilst the protease inhibitor N-phenylmaleimide provided no protective benefit, ACTH concentrations remained clinically interpretable throughout the 48-hour study window—though PPID horses showed significant decline between 4 and 8 hours, whereas healthy horses demonstrated stable readings over time. For practitioners, this work offers reassurance that ACTH samples retain diagnostic validity even with delayed processing and that expensive inhibitors or specialised centrifugation protocols are unnecessary, though the marked difference in ACTH stability between healthy and PPID populations warrants consideration when interpreting borderline results in horses with hormonal dysfunction.
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Practical Takeaways
- •ACTH samples do not require special handling or protease inhibitors to remain valid for diagnostic testing within 48 hours of collection
- •Samples can be allowed to separate by gravity rather than being centrifuged immediately, simplifying field collection protocols
- •Clinicians can send ACTH samples to reference labs without urgent processing, though PPID cases show earlier degradation and should be prioritized
Key Findings
- •ACTH concentration remained clinically useful when measured up to 48 hours after blood collection
- •Significant ACTH degradation occurred in PPID horses between 4-8 hours post-collection, but not in healthy horses
- •Plasma separation method (immediate centrifugation vs gravity separation) had no significant effect on ACTH stability (P = 0.1)
- •Addition of N-phenylmaleimide protease inhibitor provided no benefit in reducing ACTH degradation