Comparative analysis of calculating sigma metrics by a trueness verification proficiency testing-based approach and an internal quality control data inter-laboratory comparison-based approach

Introduction: Two methods were compared for evaluating the sigma metrics of clinical biochemistry tests using two different allowable total error (TEa) specifications.

Materials and methods: The imprecision (CV%) and bias (bias%) of 19 clinical biochemistry analytes were calculated using a trueness verification proficiency testing (TPT)-based approach and an internal quality control data inter-laboratory comparison (IQC)-based approach, respectively. Two sources of total allowable error (TEa), the Clinical Laboratory Improvement Amendments of 1988 (CLIA '88) and the People's Republic of China Health Industry Standard (WS/T 403-2012), were used to calculate the sigma metrics (σ_CLIA, σ_WS/T ). Sigma metrics were calculated to provide a single value for assessing the quality of each test based on a single concentration level.

Results: For both approaches, σ_CLIA > σ_WS/T in 18 out of 19 assays. For the TPT-based approach, 16 assays showed σ_CLIA > 3, and 12 assays showed σ_WS/T > 3. For the IQC-based approach, 19 and 16 assays showed σ_CLIA > 3 and σ_WS/T > 3, respectively.

Conclusions: Both methods can be used as references for calculating sigma metrics and designing QC schedules in clinical laboratories. Sigma metrics should be evaluated comprehensively by different approaches.