Nasir Nadzimah Mohd, Sthaneshwar Pavai, Yunus Putri Junaidah Megat, Yap Sook-Fan
Department of Pathology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
Malays J Pathol. 2010 Jun;32(1):21-6.
The objective of the study is to determine the level of agreement between measured total carbon dioxide (TCO2) and calculated bicarbonate (HCO3-) in our laboratory.
TCO2 and HCO3- values of 1820 samples drawn at the same time from the patient were compared. TCO2 from venous samples was measured on Dimension RxL while HCO3- was obtained from arterial blood gas samples analyzed on Radiometer ABL 700.
The TCO2 and HCO3- values correlated well (r = 0.977, p < 0.001), with the correlation given by the equation, y = 0.986x - 0.5335. Using Bland-Altman analysis, the bias was 0.87 mmol/L (SD 1.42 mmol/L), and the limits of agreement (LOA) were -1.92 to 3.67 mmol/L. Story and Poustie's criteria were applied to study the agreement between these two methods. Based on the first criterion that the bias between TCO2 and HCO3- should be less than +/- 1 mmol/L, the results for the two methods appear to be in good agreement. The second criterion requires that the LOA between the two methods should range between a bias of +/- 2 mmol/L or a total span of 4 mmol/L; the LOA was exceeded in our study. Using the total allowable error in the Bland Altman plot also showed that the two values cannot be used interchangeably especially at the lower values.
TCO2 did not show good agreement with HCO3-. Clinicians should be aware of this discrepancy and hence should be cautious when using HCO3- for management of acid-base disorders.
本研究的目的是确定我们实验室中测量的总二氧化碳（TCO2）与计算的碳酸氢盐（HCO3-）之间的一致程度。
对从患者身上同时采集的1820份样本的TCO2和HCO3-值进行比较。静脉样本中的TCO2在Dimension RxL上进行测量，而HCO3-则从在Radiometer ABL 700上分析的动脉血气样本中获得。
TCO2和HCO3-值具有良好的相关性（r = 0.977，p < 0.001），相关方程为y = 0.986x - 0.5335。使用Bland-Altman分析，偏差为0.87 mmol/L（标准差1.42 mmol/L），一致性界限（LOA）为-1.92至3.67 mmol/L。应用Story和Poustie的标准来研究这两种方法之间的一致性。基于第一个标准，即TCO2和HCO3-之间的偏差应小于+/-1 mmol/L，两种方法的结果似乎具有良好的一致性。第二个标准要求两种方法之间的LOA应在偏差+/-2 mmol/L或总范围4 mmol/L之间；在我们的研究中超出了LOA。使用Bland Altman图中的总允许误差也表明，这两个值不能互换使用，尤其是在较低值时。
TCO2与HCO3-未显示出良好的一致性。临床医生应意识到这种差异，因此在使用HCO3-管理酸碱紊乱时应谨慎。
