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Evaluation of Diagnostic Tests for Insulin Dysregulation in Adult Light-Breed Horses

Dunbar, Laura K, Dunbar
http://rave.ohiolink.edu/etdc/view?acc_num=osu1461166831

Abstract Details

2016, Master of Science, Ohio State University, Comparative and Veterinary Medicine.
Several tests have been evaluated in horses for quantifying insulin dysregulation in order to support a diagnosis of Equine Metabolic Syndrome (EMS). Comparing the performance of these tests in the same horses will provide clarification of their accuracy in the diagnosis of equine insulin dysregulation. The objective of the following investigations was to evaluate the agreement between basal serum insulin concentrations (BIC), the oral sugar test (OST), the combined glucose-insulin test (CGIT), and the frequently sampled insulin-modified intravenous glucose tolerance test (FSIGTT) in twelve healthy, light-breed horses. Each of the above tests was performed once, in randomized order on 12 adult horses, and the results were compared. Minimal Model analysis of the FSIGTT was considered the reference standard and classified 7 horses as insulin resistant (IR) and 5 as insulin sensitive (IS). In contrast, BIC and OST assessment using conventional cutoff values classified all horses as IS. Kappa coefficients, measuring agreement among BIC, OST, CGIT, and FSIGTT were poor to fair. Sensitivity of the CGIT (positive phase duration of the glucose curve > 45 minutes) was 85.7% and specificity was 40%, while CGIT ([insulin]45 > 100 µIU/ml) sensitivity and specificity were 28.5% and 100%, respectively. Area under the glucose curve (AUCg0-120) was significantly correlated among the OST, CGIT, and FSIGTT, but Bland-Altman method and Lin’s concordance coefficient showed lack of agreement. These results suggest that current criteria for diagnosis of insulin dysregulation using BIC and the OST are highly specific but lack sensitivity. The CGIT displayed better sensitivity and specificity; however, modifications may be necessary to improve agreement with Minimal Model analysis. Proxy measurements of insulin sensitivity calculated from fasting insulin and glucose concentrations have been correlated to Minimal Model analysis of the FSIGTT in horses and humans, but correlation with several morphometric parameters measured in the same cohort of equids has not been reported. Morphometric measurements (body condition score [BCS], cresty neck score [CNS], calculated body weight [BW], mean neck circumference [MNC], retroperitoneal fat depth [RFD], and tailhead fat depth [TFD]) were obtained from 12 horses in which Minimal Model analysis was performed. Proxy measurements of insulin resistance (reciprocal of the square root of insulin [RISQI], modified insulin to glucose ratio [MIRG], quantitative insulin sensitivity check index [QUICKI], insulin to glucose ratio [I:G], and homeostasis model assessment [HOMA]) were calculated. BCS, CNS, TFD, and MNC were significantly correlated with proxy measurements. However, no significant correlation was observed between morphometric data and insulin sensitivity (SI), and no significant difference was observed between insulin resistant (IR) and insulin sensitive (IS) horses with respect to morphometric parameters or proxies. Significant correlations were observed between Minimal Model parameters and proxy measurements. Many morphometric measurements correlated with proxy measurements of insulin sensitivity, and proxies were significantly correlated to SI. CNS displayed the strongest correlation to proxies, consistent with its reported utility in identification of horses at risk for EMS.
Teresa Burns (Advisor)
Ramiro Toribio (Committee Member)
James Belknap (Committee Member)
57 p.
Endocrinology; Veterinary Services

Recommended Citations

Citations

  • Dunbar, Dunbar, L. K. (2016). Evaluation of Diagnostic Tests for Insulin Dysregulation in Adult Light-Breed Horses [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461166831

    APA Style (7th edition)

  • Dunbar, Dunbar, Laura. Evaluation of Diagnostic Tests for Insulin Dysregulation in Adult Light-Breed Horses. 2016. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1461166831.

    MLA Style (8th edition)

  • Dunbar, Dunbar, Laura. "Evaluation of Diagnostic Tests for Insulin Dysregulation in Adult Light-Breed Horses." Master's thesis, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461166831

    Chicago Manual of Style (17th edition)

osu1461166831
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This open access ETD is published by The Ohio State University and OhioLINK.