Evaluation of a point-of-care electrochemical meter to detect subclinical ketosis and hypoglycaemia in lactating dairy cows

Objectives: To evaluate and validate a hand-held electrochemical meter (Precision Xtra®) as a screening test for subclinical ketosis and hypoglycaemia in lactating dairy cattle. Design: Method comparison study using a convenience sample. Procedure: Blood samples were collected into plain tubes from the coccygeal vessels of 181 Holstein cows at 2–4 weeks of lactation during summer in Iran. Blood β-hydroxybutyrate concentration (BHB) and glucose concentration were immediately measured by the electrochemical meter after applying 20 μL of blood to the reagent strip. Passing–Bablok regression and Bland-Altman plots were used to determine the accuracy of the meter against laboratory reference methods (BHB dehydrogenase and glucose oxidase). Results: Serum BHB ranged from 0.1 to 7.3 mmol/L and serum glucose ranged from 0.9 to 5.1 mmol/L. Passing–Bablok regression analysis indicated that the electrochemical meter and reference methods were linearly related for BHB and glucose, with a slope estimate that was not significantly different from 1.00. Clinically minor, but statistically significant, differences were present for the intercept value for Passing–Bablok regression analysis for BHB and glucose, and bias estimates in the Bland-Altman plots for BHB and glucose. Conclusion: The electrochemical meter provided a clinically useful method to detect subclinical ketosis and hypoglycaemia in lactating dairy cows. Compared with other method validation studies using the meter, we attributed the improved performance of the electrochemical meter to application of a fixed volume of blood (20 μL) to the reagent strip, use of the meter in hot ambient conditions and use of glucose oxidase as the reference method for glucose analysis.