title: Evaluation of 2 portable ion-selective electrode meters for determining whole blood, plasma, urine, milk, and abomasal fluid potassium concentrations in dairy cattle.
abstract: Two low-cost ion-selective electrode (ISE) handheld meters (CARDY C-131, LAQUAtwin B-731; Horiba Ltd., Albany, NY) have recently become available for measuring the potassium concentration ([K(+)]) in biological fluids. The primary objective of this study was to characterize the analytical performance of the ISE meters in measuring [K(+)] in bovine whole blood, plasma, urine, milk, and abomasal fluid. We completed 6 method comparison studies using 369 whole blood and plasma samples from 106 healthy periparturient Holstein-Friesian cows, 138 plasma samples from 27 periparturient Holstein-Friesian cows, 92 milk samples and 204 urine samples from 16 lactating Holstein-Friesian cows, and 94 abomasal fluid samples from 6 male Holstein-Friesian calves. Deming regression and Bland-Altman plots were used to characterize meter performance against reference methods (indirect ISE, Hitachi 911 and 917; inductively coupled plasma-optical emission spectroscopy). The CARDY ISE meter applied directly in plasma measured [K(+)] as being 7.3% lower than the indirect ISE reference method, consistent with the recommended adjustment of +7.5% when indirect ISE methods are used to analyze plasma. The LAQUAtwin ISE meter run in direct mode measured fat-free milk [K(+)] as being 3.6% lower than the indirect ISE reference method, consistent with a herd milk protein percentage of 3.4%. The LAQUAtwin ISE meter accurately measured abomasal fluid [K(+)] compared to the indirect ISE reference method. The LAQUAtwin ISE meter accurately measured urine [K(+)] compared to the indirect ISE reference method, but the median measured value for urine [K(+)] was 83% of the true value measured by inductively coupled plasma-optical emission spectroscopy. We conclude that the CARDY and LAQUAtwin ISE meters are practical, low-cost, rapid, accurate point-of-care instruments suitable for measuring [K(+)] in whole blood, plasma, milk, and abomasal fluid samples from cattle. Ion-selective electrode methodology is not suitable for measuring [K(+)] in bovine urine.
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.
authors.forename: A A
authors.initials: AA
authors.lastname: Megahed
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.
authors.forename: M W H
authors.initials: MWH
authors.lastname: Hiew
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.
authors.forename: W
authors.initials: W
authors.lastname: Grünberg
authors.affiliation: Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois at Urbana-Champaign 61802. Electronic address: constabl@illinois.edu.
authors.forename: P D
authors.initials: PD
authors.lastname: Constable
mesh_terms: D000018:Abomasum / Q000737:chemistry*; D000818:Animals; D001826:Body Fluids / Q000737:chemistry; D002417:Cattle / Q000378:metabolism*; D002418:Cattle Diseases / Q000097:blood / Q000175:diagnosis; D005260:Female; D007008:Hypokalemia / Q000175:diagnosis / Q000662:veterinary; D017736:Ion-Selective Electrodes; D007774:Lactation; D008297:Male; D008892:Milk / Q000737:chemistry*; D010949:Plasma / Q000737:chemistry; D019095:Point-of-Care Systems; D011188:Potassium / Q000032:analysis* / Q000097:blood / Q000652:urine
chemical_list: D011188:Potassium
keywords: hypokalemia; point-of-care