Comparison of two methods for measurement of equine adrenocorticotropin

Heidi E. Banse, Nichol Schultz, Molly McCue, Ray Geor, Dianne McFarlane

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5 Scopus citations


Accurate measurement of equine adrenocorticotropin (ACTH) is important for the diagnosis of equine pituitary pars intermedia dysfunction (PPID). Several radioimmunoassays (RIAs) and chemiluminescent immunoassays (CIAs) are used for measurement of ACTH concentration in horses; whether these methods yield similar results across a range of concentrations is not determined. We evaluated agreement between a commercial RIA and CIA. Archived plasma samples (n = 633) were measured with both assays. Correlation between the 2 methods was moderate (r = 0.49, p < 0.001). Bland–Altman analysis revealed poor agreement, with a proportional bias and widening limits of agreement with increasing values. Poor agreement between assays was also observed when evaluating plasma samples with concentrations at or below the recommended diagnostic cutoff value for PPID testing. The lack of agreement suggests that measurements obtained should not be considered interchangeable between methods.

Original languageEnglish (US)
Pages (from-to)233-237
Number of pages5
JournalJournal of Veterinary Diagnostic Investigation
Issue number2
StatePublished - Mar 1 2018


  • ACTH
  • chemiluminescent immunoassay
  • horses
  • radioimmunoassay


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