### INTRODUCTION

*u*, within-laboratory reproducibility); (2) uncertainty of the end-user calibrator (

_{Rw}*u*) obtained from the manufacturer or established by a laboratory with its own measuring system; and (3) bias correction, if a medically unacceptable measurement bias exists [4, 6, 7].

_{cal}*u*values cannot be added or subtracted, relative standard uncertainties (

*u*

_{rel}) first have to be converted to their respective variances (SD

^{2}and CV

^{2}) in calculations [6, 7, 10].

*u*calculation, MU may be overestimated. Practical considerations for when a shift occurs after a reagent lot change are reported in several guidelines [7]. However, more specific recommendations are needed, e.g., a “significant change” upon a reagent lot change has to be clearly defined. In addition, the extent of differences that such considerations can bring about when MU is calculated using real-world IQC data should be demonstrated.

_{Rw}### MATERIALS AND METHODS

### Materials

### MU estimation by different calculation methods using 1-year IQC data

*u*) values (Fig. 1):

_{Rw}*u*) was calculated as the SD, regardless of reagent lot changes [6, 7].

_{tot}*u*values calculated for each data subgroup were combined to obtain the overall uncertainty (subgrouping uncertainty,

_{Rw}*u*) according to equation (2) [6, 7, 10].

_{sub}*u*values were combined with the uncertainty of end-user calibrator values and bias uncertainty. The combined MU values were obtained according to equation (3) [7]:

_{Rw}*u*is combined uncertainty,

_{c}*u*is the standard uncertainty obtained by repetitive measurement,

_{Rw}*u*is the uncertainty of end-user calibrator, and

_{cal}*u*is the uncertainty of bias.

_{bias}*u*values were combined with the uncertainty of end-user calibrator values to obtain expanded uncertainty [6, 7]:

_{Rw}*u*) values were multiplied by 2 (coverage factor,

_{c}*k*=2) (equation 5). The expanded uncertainty values were expressed as the standard expanded uncertainty (

*U*) with their units and relative expanded uncertainty (%

*U*) [6, 7, 10].

_{rel}### Monte Carlo simulation (MCS) of a reagent lot change using artificial IQC data

### Comparison of two IQC datasets from different QC material lots

### Outlier elimination

### Statistical analysis

*t*-tests, and F-tests, were performed using Microsoft Excel 365 (Microsoft, Redmond, WA, USA). Data normality and distribution skewness and kurtosis were analyzed using RStudio (PBC, Boston, MA, USA). An absolute skewness value ≤2 or an absolute kurtosis (excess) ≤4 was used as a threshold for determining considerable normality [12, 13].

### RESULTS

### Comparison of MU data obtained via different calculation methods using 1-year IQC data

*U*values calculated by subgrouping (%

_{rel}*U*) were lower than the values calculated as a whole (%

_{rel_sub}*U*); the mean values of %

_{rel_tot}*U*and %

_{rel_sub}*U*were 5.45 and 5.62 at level 1 and 4.95 and 5.07 at level 2, respectively (Table 1). The entire calculation process and MU values for each analyte are listed in Supplemental Data Table S3 (A-N). The mean MU differences (%, %

_{rel_tot}*U*−%

_{rel_sub}*U*) were -0.13% at level 1 (range, -0.88 to -2.43×10-5%) and -0.12% at level 2 (range, -0.77 to -2.20×10

_{rel_tot}^{-5}%; Fig. 3).

### MCS of a reagent lot change using artificial IQC data

*U*values were relatively constant, irrespective of the degree of shift. However, %

_{sub}*U*values increased with increasing degree of shift in both directions. The mean MU differences (%, %

_{sub}*U*–%

_{rel_sub}*U*) gradually increased as the mean differences (shifts) increased (Fig. 4B).

_{rel_tot}### Review and comparative analysis of IQC data using two different QC material lots

*t*-test (for mean comparison) and F-test (for variance [SD] comparison) were used to analyze the significance of differences between the IQC datasets (Table 2). The mean values were significantly different at all levels for all analytes except creatinine. Additionally, SDs were significantly different for most analytes (except AST, LDL, creatinine, total protein, and BUN at level 1 and albumin, AST, and creatinine at level 2).

### DISCUSSION

*U*) calculated by subgrouping of the data would be substantially lower than those calculated as a whole (%

_{sub}*U*). However, the differences between MU values obtained by the two different calculation methods were minimal (minimum difference: 7.13×10-5%, maximum difference: 0.825%), although the %

_{tot}*U*values were lower for all analytes.

_{sub}*U*, relative expansion uncertainty,

_{rel}*k*=2) (Fig. 4B). When we comparatively evaluated reagent lot changes in the laboratory, the predefined allowable total error was used as an acceptable performance criterion [16]. If we presume that the mean difference after a lot change was 8%, which is within the acceptable interval, the new lot would be used without further evaluation. However, in MU estimation, a significant difference was observed depending on the calculation method used. The MU value calculated regardless of the shift of 8% was higher (

*u*=4.34) than that calculated considering the shift (

_{tot}*u*=1.7), which led to a highly overestimated MU value.

_{sub}