Immunoreactive insulin stability in horses at risk of insulin dysregulation

• Published in: Journal of veterinary internal medicine Vol. 33; no. 6; pp. 2746 - 2751
• Main Authors: Leschke, Dakota H., Muir, Genevieve S., Hodgson, Jack K., Coyle, Mitchell, Horn, Remona, Bertin, François‐René
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.11.2019; Wiley
• Subjects: adults; Animals; blood sampling; blood serum; Blood Specimen Collection - veterinary; body condition; chemiluminescent assay; diagnostic testing; EDTA (chelating agent); endocrinology; EQUID; equine metabolic syndrome; Ethics; Female; Glucose; Horse Diseases - blood; Horses; Immunoassay; insulin; Insulin - blood; Insulin - metabolism; Insulin resistance; laminitis; linear models; luminescent assay; Male; Metabolic syndrome; Metabolic Syndrome - veterinary; obesity; Pituitary Diseases - blood; Pituitary Diseases - veterinary; Pituitary Gland, Intermediate; Plasma; prospective studies; risk assessment; storage temperature; Studies; Testing laboratories; Australia; Victoria Australia; equine metabolic syndrome; chemiluminescent assay; diagnostic testing; laminitis; obesity; endocrinology
• ISSN: 0891-6640; 1939-1676; 1939-1676
• DOI: 10.1111/jvim.15629

Background Diseases associated with insulin dysregulation (ID), such as equine metabolic syndrome and pituitary pars intermedia dysfunction, are of interest to practitioners because of their association with laminitis. Accurate insulin concentration assessment is critical in diagnosing and managing these diseases. Hypothesis/Objectives To determine the effect of time, temperature, and collection tube type on insulin concentrations in horses at risk of ID. Animals Eight adult horses with body condition score >6/9. Methods In this prospective study, subjects underwent an infeed oral glucose test 2 hours before blood collection. Blood samples were divided into ethylenediaminetetraacetic acid, heparinized, or serum tubes and stored at 4 or 20°C. Tubes were centrifuged and analyzed for insulin by a chemiluminescent assay over 8 days. Changes in insulin concentrations were compared with a linear mixed effects model. Results An overall effect of time, tube type and temperature was identified (P = .01, P = 0.001, and P = 0.001, respectively). Serum and heparinized samples had similar concentrations for 3 days at 20°C and 8 days at 4°C; however, after 3 days at 20°C, heparinized samples had significantly higher insulin concentrations (P = .004, P = .03, and P = .03 on consecutive days). Ethylenediaminetetraacetic acid samples had significantly lower insulin concentrations regardless of time and temperature (P = .001 for all comparisons). Conclusions and Clinical Importance These results suggest an ideal protocol to determine insulin concentrations involves using serum or heparinized samples with analysis occurring within 3 days at 20°C or 8 days at 4°C.