Background: Sigma metrics are commonly used to evaluate laboratory management. In this study, we aimed to evaluate the analytical performance of cystatin C using sigma metrics and to develop an individualized quality control scheme for cystatin C levels.

Methods: Bias was calculated based on the samples used for the external quality assessment. The coefficient of variation was calculated using 6 months of internal quality control (IQC) measurements at two levels, and desirable specification derived from biological variation was used as the quality goal. The sigma value for cystatin C was calculated using the above data. The IQC scheme and improvement measures were formulated according to the Westgard sigma standards for batch size and quality goal index (QGI).

Results: The sigma values for cystatin C, for quality control levels 1 and 2, were 3.04 and 4.95, respectively. The 13s/22s/R4s/41s/8x multi-rules (N=4 or 2 with R=2 or 4), with a batch size of 45 patient samples, were selected as the IQC schemes for cystatin C. With different levels of cystatin C, the power function graph showed a probability for error detection of 94% and 100% and a probability for false rejection of 4% and 2%, respectively. According to the QGI of cystatin C, its precision needs to be improved.

Conclusions: With a “desirable” biological variation of 6.50%, the Westgard rule 13s/22s/R4s/41s/8x (N=4 or 2 with R=2 or 4, batch size of 45) with high efficacy for determining the detection error is recommended for individualized quality control schemes of cystatin C.

背景：Sigma度量标准通常用于评估实验室管理。在这项研究中，我们旨在评估使用sigma度量标准的半胱氨酸蛋白酶抑制剂C的分析性能，并针对半胱氨酸蛋白酶抑制剂C水平制定个性化的质量控制方案。

方法：根据用于外部质量评估的样品计算偏差。使用六个月的两个阶段的内部质量控制（IQC）测量来计算变异系数，并将源自生物学变异的理想指标用作质量目标。使用以上数据计算半胱氨酸蛋白酶抑制剂C的sigma值。IQC方案和改进措施是根据Westgard sigma标准制定的批次大小和质量目标指数（QGI）。

结果：对于质量控制水平1和2，半胱氨酸蛋白酶抑制剂C的sigma值分别为3.04和4.95。选择批次大小为45个患者样本的13s / 22s / R4s / 41s / 8x多规则（N = 4或2，R = 2或4）作为半胱氨酸蛋白酶抑制剂C的IQC方案。功率函数图显示的错误检测概率分别为94％和100％，错误拒绝的概率分别为4％和2％。根据胱抑素C的QGI，其精度需要提高。

结论：具有“理想”的感觉 生物学变异为6.50％，Westgard规则13s / 22s / R4s / 41s / 8x（N = 4或2，R = 2或4，批次大小为45）具有较高的检测误差效率，建议用于个性化质量控制胱抑素C的方案