Time but not storage of equine plasma in silicate-coated tubes affects adrenocorticotropic hormone stability.

This research investigates the relationship between time, storage method, and the stability of the hormone adrenocorticotropic hormone (ACTH) in horse blood samples. The study finds that time between blood collection and analysis impacts the measured ACTH concentrations and, therefore, can affect diagnosis accuracy, but the storage of plasma in serum tubes showed no significant effect on ACTH levels.

Study Background

• The research focuses on the condition Pituitary Pars Intermedia Dysfunction (PPID) in horses, which is often diagnosed by measuring ACTH concentrations in the blood.
• Because it is believed that ACTH is unstable, it is typically recommended to transfer the centrifuged plasma into cryovials, specially formatted tubes designed for keeping biological samples at very low temperatures.
• In real-world practise, however, serum (red-top) tubes are often used as an alternative to cryovials so this study aimed to investigate whether this substitute storage method has any effect on the stability of ACTH concentrations and consequently, on the diagnosis of PPID.

Methodology

• Blood was extracted from 16 horses (9 with PPID and 7 control horses) and stored in EDTA tubes. After centrifugation, plasma was distributed either into a cryovial or into a serum tube.
• The samples were then stored at two different temperatures (4 and 20 °C), and ACTH concentrations were measured after 2, 24, and 48 hours using a chemiluminescent assay.
• Statistical analysis was conducted using a 2-way repeated measures ANOVA to assess the influence of time and storage conditions on ACTH concentrations.

Findings

• The study revealed that there was a significant effect of time on ACTH concentrations in horses at both 4 and 20 °C. ACTH levels decreased over time in serum samples and within the PPID horse group.
• However, no significant effect of storing plasma in a serum tube was detected, as opposed to cryovials, showing that the container used for storage does not necessarily affect ACTH stability.
• It was found that three horses diagnosed with PPID would have been categorised differently if the samples had experienced a delay of 24 or 48 hours before analysis.

Conclusion

• Time, not the storage method, decreases the ACTH concentration measured in horses with PPID. The time delay between sample acquisition and analysis may potentially lead to incorrect diagnoses.
• There was no significant difference detected in ACTH stability when plasma was stored in serum tubes versus cryovials.