Synthetic adrenocorticotropic hormone stimulation tests in healthy neonatal foals.
Authors: Hart Kelsey A, Ferguson Duncan C, Heusner Gary L, Barton Michelle Henry
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: ACTH Stimulation Testing in Neonatal Foals Adrenal insufficiency in critically ill neonates represents a significant diagnostic challenge in equine practice, yet the optimal dose and protocol for ACTH stimulation testing—a well-established diagnostic tool in human medicine—had not been formally evaluated in foals. Hart and colleagues administered four different doses of cosyntropin (synthetic ACTH: 1, 10, 100, and 250 µg) intravenously to 14 healthy neonatal foals aged 3–4 days, collecting blood samples over 150 minutes to determine the cortisol response pattern at each dose. The 1 µg dose produced no significant cortisol elevation, whilst the 10 µg dose peaked at 30 minutes before returning to baseline by 90 minutes; in contrast, both 100 and 250 µg doses showed delayed peak responses at 90 minutes with significantly higher cortisol concentrations than the 10 µg dose at that timepoint, though no meaningful difference existed between the 100 and 250 µg responses. For equine practitioners assessing adrenal function in sick neonatal foals, these findings establish that either 10 or 100 µg cosyntropin represents an appropriate testing dose, with the choice likely depending on clinical context and whether a rapid (10 µg) or more sustained cortisol response profile is preferred for diagnostic purposes.
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Practical Takeaways
- •For neonatal foal adrenal function assessment, use either 10 or 100 microgram cosyntropin doses; 1 microgram is insufficient to stimulate response
- •Timing of cortisol peak varies by dose (30 minutes for 10 micrograms, 90 minutes for higher doses), so blood sampling protocols must account for this difference
- •The 10 microgram dose may be preferable as a lower-dose test analogous to human critical illness protocols, with cortisol measured at 30 minutes post-administration
Key Findings
- •Serum cortisol did not significantly increase after 1 microgram cosyntropin administration in neonatal foals
- •Peak cortisol occurred at 30 minutes after 10 microgram dose but at 90 minutes after 100 and 250 microgram doses
- •100 and 250 microgram doses induced significantly greater cortisol concentrations at 90 minutes compared to 10 microgram dose
- •No significant difference in area under the cortisol curve between 100 and 250 microgram doses, suggesting dose plateau effect