Effect of thyrotropin-releasing hormone stimulation testing on the oral sugar test in horses when performed as a combined protocol.

Elizabeth Hodge, Alycia Kowalski, Catherine Torcivia, Sue Lindborg, Darko Stefanovski, Kelsey Hart, Nicholas Frank, Andrew van Eps

Journal of veterinary internal medicine 2019 Sep

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The use of parallel dynamic tests to identify insulin dysregulation (ID) and pituitary pars intermedia dysfunction (PPID) in horses could have better diagnostic utility than measuring baseline hormone concentrations, if the tests do not alter diagnostic interpretation of one another. Performing a thyrotropin-releasing hormone (TRH) stimulation test before an oral sugar test (OST) would not affect results of OST. Twenty-six healthy university-owned horses. A prospective randomized placebo-controlled, crossover design was used to evaluate 3 OST protocols: OST alone, TRH followed by OST (TRH + OST), and placebo followed by OST (placebo + OST). Agreement for plasma insulin concentrations and diagnostic interpretation were assessed with Bland-Altman and logistic regression analyses, respectively. Bland-Altman analysis of TRH + OST versus OST alone showed good agreement between testing protocols, with bias ± SD for insulin concentrations at baseline 0.4 ± 4.7 μIU/mL (95% limits of agreement [LOA], -8.8 to 9.7), 60 minute -0.5 ± 22.6 μIU/mL (95% LOA, -44.7 to 43.8), and 90 minute 1.9 ± 20.6 μIU/mL (95% LOA, -38.5 to 42.4) after OST, similar to placebo + OST versus OST alone. Diagnostic interpretation (positive/negative) was not different between protocols (TRH + OST versus OST alone [P = .78], placebo + OST versus OST alone [P = .77], or TRH + OST versus placebo + OST [P = .57]). Concurrent testing for PPID and ID with a TRH stimulation test before an OST is an acceptable diagnostic tool for investigation of endocrinopathies in horses and allows accurate testing to be performed efficiently in 1 visit. © 2019 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.

Citation

Elizabeth Hodge, Alycia Kowalski, Catherine Torcivia, Sue Lindborg, Darko Stefanovski, Kelsey Hart, Nicholas Frank, Andrew van Eps. Effect of thyrotropin-releasing hormone stimulation testing on the oral sugar test in horses when performed as a combined protocol. Journal of veterinary internal medicine. 2019 Sep;33(5):2272-2279