Collecting equine whole blood in glass tubes does not decrease adrenocorticotropic hormone concentration compared to plastic tubes.

Abstract

OBJECTIVE: Pituitary pars intermedia dysfunction is diagnosed using immunoreactive ACTH concentrations. Glass reportedly binds ACTH, but the clinical relevance of using glass blood tubes for measuring equine ACTH concentrations is controversial. This study investigates whether the collection of whole blood into glass EDTA tubes and storage for up to 6 hours changes ACTH concentrations compared to plastic EDTA tubes. METHODS: This was a cohort study. Whole blood was collected into both glass and plastic EDTA tubes from 9 horses > 12 years of age, including 4 with pituitary pars intermedia dysfunction and 5 controls. Samples were centrifuged immediately or stored in the collection tube at 4 &#xb0;C for 2, 4, or 6 hours before centrifugation. Plasma was separated into cryovials, and immunoreactive ACTH was immediately measured on a chemiluminescent assay. Data were analyzed using a 2-way repeated-measures ANOVA with P < .05 considered significant. RESULTS: Neither tube type nor storage time had a significant effect on plasma immunoreactive ACTH concentration. CONCLUSIONS: When stored at 4 &#xb0;C as whole blood on glass for up to 6 hours, equine immunoreactive ACTH concentrations do not significantly differ from collection and storage on plastic. CLINICAL RELEVANCE: Both glass and plastic EDTA tubes can be used for collection and same-day analysis of immunoreactive ACTH concentrations.