Background: We compared the effect of haemolysis in sodium measurement using indirect and direct ion-selective electrodes (ISE) to test the hypothesis that haemolytic effect on sodium would be greater with indirect ISE due to electrolyte exclusion effect (EEE) from released intracellular proteins.

Methods: Plasma lithium heparin samples (n=36) from four volunteers were prepared to give a range of haemolytic indices (H-indices). Samples were analysed for sodium by indirect ISE, H-index and total protein on an Abbott Architect c16000 and sodium by direct ISE on a Siemens RAPIDPoint 500. Percentage changes in sodium in paired direct and indirect ISE values were compared.

Results: Abbott H-index, which represents haemoglobin concentration in g/L, correlated with percentage negative change in sodium by direct ISE (ρ 0.995, P<0.001) and indirect ISE (ρ 0.991, P<0.001). Percentage negative change was less when sodium was measured by direct ISE compared to indirect ISE (Wilcoxon signed-rank Z=3.46, P=0.01). The difference in percentage change in sodium between direct ISE and indirect ISE correlated with total protein (ρ 0.751, P<0.001). The negative bias in sodium results exceeded the reference change value of 2.2% at an H-index of 8.31 for indirect ISE and 9.26 for direct ISE.

Conclusion: Haemolysis causes negative influence with sodium measured by both indirect and direct ISE due to a dilutional hyponatremia. The additional interference in indirect ISE is due to the EEE but this is unlikely to be clinically significant as it is small in magnitude.

背景：我们比较了使用间接和直接离子选择电极（ISE）进行溶血在钠测量中的效果，以检验以下假设的假设：由于释放的细胞内蛋白质中的电解质排斥效应（EEE），使用间接ISE对钠的溶血作用会更大。

方法：准备了来自四名志愿者的血浆肝素锂样品（n = 36），以给出一系列的溶血指数（H-indices）。通过间接ISE分析样品中的钠，在Abbott Architect c16000上分析H指数和总蛋白，在Siemens RAPIDPoint 500上通过直接ISE分析钠。比较成对的直接和间接ISE值中钠的百分比变化。

结果：代表以g / L表示的血红蛋白浓度的雅培H指数与直接ISE（Ï≥0.995，P <0.001）和间接ISE（Ï≥0.991，P <0.001）引起的钠负变化百分比相关。与直接ISE相比，直接ISE测量钠的负变化百分率更低（Wilcoxon带符号秩Z = 3.46，P = 0.01）。直接ISE和间接ISE之间钠的百分比变化差异与总蛋白相关（??? 0.751，P <0.001）。钠含量的负偏差在间接ISE的H指数为8.31，直接ISE的9.26时超过了参考变化值2.2％。

结论：由于稀释性低钠血症，通过间接和直接ISE测量的溶血均对钠造成负面影响。间接ISE中的额外干扰是由于EEE引起的，但是由于其幅度较小，因此在临床上不太可能产生重大影响。