The six sigma model was used to evaluate the analytical performance of glycosylated hemoglobin (HbA_1c), and the internal quality control (IQC) strategy and quality improvement measures for the HbA_1c was initially established.

The data of external quality assessment (EQA) of HbA_1c from National Center for Clinical Laboratories (NCCL) in 2020 and its IQC data of the two concentration levels from January to June 2020 were collected. And based on the allowable total error (TEa) from four different sources to calculate the sigma level of HbA_1c respectively. Meanwhile, analytical performance of HbA_1c was demonstrated on the standardized sigma performance verification chart. According to the Westgard sigma rule flow chart with batch length and quality goal index (QGI), IQC strategy and quality improvement plan of the HbA_1c were formulated.

The analytical performance of HbA_1c was at the "world-class" level based on the Spanish EQA standard and the German RiliBAK standard, while the quality goals were based on the "desirable" biological variation and EQA standard of China, analytical performance of HbA_1c was at the "unacceptable" and "excellent" levels, respectively. This study was based on EQA standard of China as the quality goal, and combined with the Westgard sigma rule with batch length, and initially established the following IQC strategy: 1_3s/2_2s/R_4s multiple rules (N=2) with batch length of 450 samples was selected as the IQC strategy for HbA_1c. Besides, the calculation of QGI showed that the bias of HbA_1c was the main factor affecting its analytical performance, and it was necessary to prioritize the formulation of corresponding improvement measures in terms of accuracy.

The six sigma model can objectively evaluate the analytical performance of HbA_1c, and has important guiding significance in the design of laboratory quality control strategies and the improvement of detection quality.