Cristol J-P, Balint B, Canaud B, Daurés M-F
Laboratoire de biochimie, CHU de/Montpellier, Hôpital Lapeyronie, 371 Avenue du Doyen Gaston Giraud, 34295 Montpellier cedex 5, France.
Nephrol Ther. 2007 Sep;3 Suppl 2:S104-11. doi: 10.1016/s1769-7255(07)80017-4.
Electrolyte disorders are frequently observed in nephrology and intensive care unit department and Na determination is routinely performed in biochemistry laboratories. Three methods are currently available. Flame photometry remains the reference method. With this method the serum sample is diluted before the actual measurement is obtained. Results are expressed as molarity (per Liter of plasma). Potentiometric methods have an increasing importance due to the advances in ion sensitive (selective) electrodes (ISE). Whereas the instruments for routine chemical analysis typically use indirect potentiometry (involving te dilution of samples) to measure sodium levels, the equipment for measuring arterial blood gases use direct potentiometry without any dilution. Thus, results obtained with indirect potentiometry are expressed in molarity (per liter of plasma) while results obtained with direct potentiometry are initially given in morality (per kg of plasma water) then converted in molarity. Analytical performances are in all cases satisfactory and therefore all the methods could be used in both normal and pathological ranges. Methods involving sample dilution such as flame photometry or indirect potentiometry, the serum sodium value would be expected to be low in case of decrease plasma water (pseudohyponatremia). By contrast, with direct potentiometry where no sample dilution takes place, no interference would be expected since the activity of sodium in the water phase only is being measured. Thus, the classical pseudohyponatremia observed with hyperlipemia or paraproteinemia are not further observed with direct potentiometry. These differences in methodology should be taken into account to explain discrepancies between results obtained with classical biochemistry analyser and with blood gas apparatus.
电解质紊乱在肾脏病科和重症监护病房很常见，血清钠测定在生化实验室是常规操作。目前有三种方法。火焰光度法仍是参考方法。使用这种方法时，血清样本在实际测量前需进行稀释。结果以摩尔浓度（每升血浆）表示。由于离子敏感（选择性）电极（ISE）的进展，电位分析法的重要性日益增加。常规化学分析仪器通常使用间接电位法（涉及样本稀释）来测量钠水平，而测量动脉血气的设备则使用直接电位法，无需任何稀释。因此，间接电位法得到的结果以摩尔浓度（每升血浆）表示，而直接电位法得到的结果最初以质量摩尔浓度（每千克血浆水）给出，然后转换为摩尔浓度。在所有情况下，分析性能都令人满意，因此所有方法都可用于正常和病理范围。对于涉及样本稀释的方法，如火焰光度法或间接电位法，在血浆水减少（假性低钠血症）的情况下，血清钠值预计会偏低。相比之下，在不进行样本稀释的直接电位法中，由于仅测量水相中钠的活性，预计不会有干扰。因此，在直接电位法中不会再观察到高脂血症或副蛋白血症时出现的典型假性低钠血症。在解释传统生化分析仪和血气分析仪所得结果之间的差异时，应考虑到这些方法学上的差异。
