The main objective of this study was to assess the comparability and interchangeability of our existing Sysmex XN-1500 hematology analyzer and the newly purchased Cell-Dyn Emerald 22 AL hematology analyzer. The results have shown a very good correlation and agreement between the Sysmex XN-1500, and the newly purchased automated Cell-Dyn Emerald 22 AL analyzer for almost all the clinically relevant main full blood count parameters. Generally, Sysmex and Abbott analyzers are comparable and interchangeable in routine diagnostic haematology laboratories, and this is evident in several studies comparing different haematological analyzers (17–19). The MCHC and PDW calculated values were not considered for the Bland-Altman analysis as no correlation/relationship between the two analyzers was found during the correlation and regression analysis. This finding is consistent with the results of Malecka and Ciepiela's study which found a significant difference between Sysmex-XN 2000 and Yumizen H2500 automated analyzers for MCHC and PDW calculated full blood count parameters (31). Hence, our findings suggest that the two analyzers cannot be used interchangeably for MCHC and PDW, albeit the clinical relevance of the latter is still under investigation(20).
Since correlation analysis may not necessarily depict agreement between two analyzers, a Bland-Altman analysis was conducted (14). The bland-Altman analysis is a statistical approach to quantify the agreement between two quantitative analyzers by constructing limits of agreement introduced by Bland and Altman in 1983. Bland-Altman plot is used to detect the presence of systematic differences between the measurements (i.e., fixed bias) or possible outliers(21). Despite our results showing very good agreement between the two analyzers, the bias for MCV, MCH, MCHC, PDW, and MPV falls outside our clinically acceptable bias range (predefined a priori). Hence, their results should be interpreted with caution, preferably using a locally established equipment-specific reference interval. Among these parameters, MCV is the most useful full blood count parameter in clinical decision-making. MCV is used to estimate the mean volume of RBCs in a sample and is a useful parameter to classify anemias based on RBC size as microcytic (MCV < 80fL), normocytic (MCV: 80-100fL), and macrocytic anemia (MCV > 100fL). The reference interval for the MCV is generally reported as 80–100 fL, but this varies by age, gender, technology, and reference population(22–24). Depending on the instrument technology, the MCV can be determined automatically when the RBC is being counted or calculated using the RBC count and the HCT(25). The MCV disagreement between the two analyzers based on Bland-Altman analysis is understandable as the MCV is directly measured by Cell-Dyn Emerald whilst calculated by Sysmex XN-series from measured RBC count and HCT results. Interestingly, MCH, MCHC, MPV, and PDW are not directly measured but are calculated parameters. The software used for the calculation of these parameters could have resulted in a significant bias in our results(26–28).
A precision study in the form of repeatability and intermediate precision was performed to assess the stability of measured full blood count parameters (red blood cells, hemoglobin, white blood cells, platelets, and mean cell volume/hematocrit) as part of the performance evaluation. In our hematology laboratory, the sample retention period is one week as our previous mini-lab laboratory study showed that full blood count parameters are stable for six days provided the blood sample is stored at a chilled temperature (2 to 8oC). Using the coefficient of variation, our result showed very good stability of all the measurable full blood count parameters for both analyzers as the CVs conformed with the manufacturer’s CV and CLSI guidelines(9). However, the coefficient of variation for Cell-Dyn Emerald 22 AL WBC result was significantly high during intermediate precision. This significant decrease in total WBC count could be the result of a drastic decrease in a particular subpopulation of WBCs as shown in a previous study that the WBC subpopulations changed over time with a decrease in eosinophils and lymphocytes and an increase in neutrophils at 2–8°C. Furthermore, the stability of WBC subpopulations was significantly different among Bayer Advia 120, Beckman Coulter LH 750, and Sysmex XE 2100 with some analytes only displaying a stability of 4h(29, 30). A sample stored beyond 24 hours at a chilled temperature would not be suitable for total white blood cell counting.
Unlike Sysmex XN-1500, our study could not assess and compare the flagging characteristics of the two analyzers as the Cell-Dyn Emerald 22 AL does not possess the technology to assess the morphological changes of cellular components of blood. Furthermore Cell-Dyn Emerald 22 AL lacks the measurement technology for reticulocytes and nucleated red blood cell counting, hence the agreement between the two analyzers using Bland-Altman analysis for these two parameters could not be assessed(3–5, 8, 19).