DETERMINATION OF POTASSIUM BY DRY REAGENT CARRIER TECHNOLOGY - A MULTICENTER EVALUATION

We describe the construction, the reaction principle and the performan ce of Reflotron(R) K+, a new Reflotron(R) test for the quantitative de termination of potassium in serum and heparinized plasma. The reaction principle is based on the introduction of the potassium cation via va linomycin into a non-polar phase; the accompanying loss of protons fro m the non-polar phase is detected by the colour change of a pH indicat or. The multicentre evaluation of the reagent carrier system showed in median CVs of < 0.9% (within-series in heparinized plasmas) and 1.3% (run-to-run in control sera). The recovery in control sera was +/- 4% for seven laboratories. In the method comparison with flame emission s pectrometry, using sera and heparinized plasma samples, regression ana lysis yielded correlations with slopes of 1.00 +/- 0.04 (median slope 1.005) and negligible intercepts. The reagent carrier system showed a linear response in the measuring range 2-12 mmol/l. Bilirubin (up to 5 13 mumol/1), triacylglycerols (up to 5,7 mmol/1), sodium (135-189 mmol /1) and ammonium ions (up to 590 mumol/1) did not interfere with the t est. Comparison with the results from flame atomic emission spectromet ry shows that the recoveries of Reflotron(R) K+ and the direct potenti ometric method are slightly and similarly influenced by total protein. With a panel of 28 drugs tested, no interference could be detected. R eflotron(R) K+ provides a precise and reliable procedure for the measu rement of potassium in serum and heparinized plasma.