Czaban J D, Cormier A D, Legg K D
Clin Chem. 1982 Sep;28(9):1936-45.
The observed reference ranges for sodium and potassium as determined by direct potentiometry vary from instrument to instrument, depending on the composition of the calibration standards. To resolve the existing confusion as to which reference intervals are most appropriately considered "normal," we propose a straightforward convention (based on plasma-water concentration units) in which the difference between direct (undiluted sample) and indirect (diluted sample) methodologies is accounted for by the volume displacement effect of proteins, lipids, and other dissolved substances in a typical plasma sample. Thus, the proposed reference intervals for sodium and potassium are approximately 7% greater by direct potentiometry than by procedures involving dilution. Data consistent with this convention can be obtained with a variety of aqueous-based calibrants, provided care is taken to minimize the errors resulting from activity coefficient and liquid junction potential effects. Additional experimental results are presented to show that these effects also account for the apparent suppression of the sodium ion concentration observed in the presence of bicarbonate ion.
通过直接电位法测定的钠和钾的观察参考范围因仪器而异，这取决于校准标准品的组成。为了解决关于哪些参考区间最适合被视为“正常”的现有混淆，我们提出了一个简单的惯例（基于血浆水浓度单位），其中直接（未稀释样品）和间接（稀释样品）方法之间的差异通过典型血浆样品中蛋白质、脂质和其他溶解物质的体积置换效应来解释。因此，通过直接电位法测定的钠和钾的建议参考区间比涉及稀释的方法大约高7%。只要注意尽量减少活度系数和液接电位效应导致的误差，使用各种水基校准物就可以获得与该惯例一致的数据。还给出了额外的实验结果，以表明这些效应也解释了在存在碳酸氢根离子的情况下观察到的钠离子浓度的明显抑制。
