Evaluation of a portable ion-selective electrode meter for measuring potassium concentrations in whole blood and plasma of calves

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.