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Trefz, F. M.; Lorenz, I.; Constable, P. D. (2018): Evaluation of a portable ion-selective electrode meter for measuring potassium concentrations in whole blood and plasma of calves. In: Veterinary Journal, Vol. 238: pp. 10-14
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An ion-selective electrode (ISE) handheld meter (LAQUAtwin B-731;Horiba) has recently become available for the measurement of potassium concentrations [K+] in biological fluids. The ISE meter has the potential to facilitate the diagnosis and treatment of potassium balance disorders of critically ill cattle. The objective of this study was to characterise the analytical performance of the ISE meter in a study sample of hospitalised calves with a broad range of plasma [K+]. For the purpose of the study, whole blood and plasma samples from 125 calves (age <= 3 months) were used for analysis. The accuracy of the meter against the reference method (indirect ISE, Cobas c 311, Roche) was assessed using Passing-Bablok regression and Bland-Altman plots. The [K+] in whole blood as measured by the ISE meter in direct mode ranged from 2.4 to 9.9 mmol/L. The meter measured whole blood [K+] as 3.8% higher than plasma [K+]. Passing-Bablok regression for whole blood [K+] measured by the meter against plasma [K+] determined by indirect potentiometry revealed a linear relationship that was almost identical to the line of identity. However, the Bland-Altman plot indicated that the meter measured plasma [K+] 5.1% lower than the reference method. This result was consistent with analytical differences of direct and indirect ISE methods in respect to variation in the plasma protein concentration. In conclusion, the LAQUAtwin B-731 meter provides an accurate, rapid and low-cost tool for the diagnosis of potassium derangements in critically ill calves, particularly when whole blood samples are analysed.