Application of Sigma Metrics for the Optimization of Quality Control Program in the Clinical Chemistry Laboratory.

Background: This study aimed to assess and optimize the quality control (QC) program in the clinical chemistry laboratory by addressing the errors after identification with Sigma metric.

Methods: All quality indicators from the internal and external quality control of 41 clinical analytes were collected in our laboratory in 2023. The Sigma metric imprecision and bias were calculated by using internal and external quality control data, respectively, then the Sigma metric and quality goal index (QGI) was calculated to assess and improve the performance of laboratory process system.

Results: Sigma levels from 21 clinical analytes were found ≥ 6, and the analytical performance of these analytes were at "world-class" level. The analytical performance of serum potassium, glucose, bicarbonate, β2-MG, LDH, and direct bilirubin reached "excellent" level (5 ≤ σ < 6 and QGI ≤ 0.8), and multiple rules of 13s22sR4s (N = 2, R = 1) with batch length of 450 patient samples were selected as QC schemes. The analytical performance of sodium and TBA also achieved "good" level (4 ≤ σ < 5 and QGI ≤ 0.8), so multiple rules of 13s22sR4s41s (N = 4, R = 1 or N = 2, R = 2) with batch length of 200 patient samples were selected as QC schemes. Sigma level of chloride, total protein, total bilirubin, and albumin was < 4 and ≥ 3 (QGI ≤ 0.8), so multiple rules of 13s22sR4s41s8x (N = 4, R = 2 or N = 2, R = 4) with batch length of 45 patient samples were selected as QC schemes. For the rest of the analytes, such as calcium and Urea, Sigma metric was found < 3, and they required more modification in quality control procedure.

Conclusions: Application of Sigma metric provided us an assessment of performance of laboratory process system and improvement of QC procedure for clinical analytes.