An improved candidate reference method for serum potassium measurement by inductively coupled plasma-mass spectrometry.

Abstract Background In 2002, the National Institute of Standards and Technology (NIST) established a reference method for serum potassium based on inductively coupled plasma-mass spectrometry (ICP-MS). The aim of this study was to develop an inexpensive and improved candidate reference method for accurate and precise determination of serum potassium. Methods Serum samples were diluted with 1% HNO 3 supplemented with 59 Cobalt as isotope internal standard, and potassium was measured by ICP-MS. The new method was evaluated with NIST standard reference materials (SRMs), according to the Clinical and Laboratory Standard Institute's evaluation protocols. Results At 4.300 and 4.678 mmol/l levels, the present method demonstrated analytical imprecision of 0.09% and 0.14%, and recoveries of 99.67% to 99.88%, respectively. The bias between the target values of SRMs were − 0.02% to + 0.28%, respectively. This method was linear between 0.0000 and 6.87 mmol/l (R 2  = 1.000). The method had an uncertainty (U 95% ) of 0.76%. Conclusions The proposed ICP-MS method to measure serum potassium is precise and accurate, with high sensitivity and specificity. It may be considered as a candidate reference method for the determination of serum potassium.