A comparison of methodologies for measuring glucose concentrations in the horse1

Five methods of measuring glucose in the horse were compared with plasma glucose reference values generated with an Autoanalyzer3 (Seal Analytical Ltd., Hampshire, UK). Plasma glucose was measured with a One Touch Ultra (LifeScan, Milpitas, CA) hand-held glucose meter and a YSI 2300 Stat Plus Glucose and Lactate Analyzer (YSI; YSI Inc., Yellow Springs, OH). Glucose also was measured in whole blood using One Touch Ultra and YSI. Finally, interstitial glucose measurements were obtained with a SEVEN continuous glucose monitoring device (Dexcom, San Diego, CA). Glucose measurements were obtained on 2 consecutive days in 6 American Quarter Horses maintained on native prairie hay and water. Each morning, 2 baseline glucose measurements were obtained 30 min apart. After a meal of sweet feed, glucose measurements were obtained every 30 min for 4 h. Patterns of postprandial glucose increases and subsequent decreases were similar across all methods but were displaced vertically from one another. Of the 5 methods, the YSI method with plasma appeared to have the best reproducibility of Autoanalyzer3 glucose values based on a random coefficients model with intercept not statistically different from zero (P = 0.08) and slope not statistically different from one (P = 0.08) and by having the highest Lin's concordance coefficient (r = 0.77). The other methods had biased random coefficients models with intercepts not equal to zero (P > 0.05) and slopes not equal to one (P > 0.05) and Lin's concordance coefficient values that ranged from 0.39 to 0.64. Technical difficulties with the SEVEN device limited its utility as a reliable method for evaluating glucose in the equine.