Analysis of process sigma values calculated from different quality control material data

Introduction: Clinical laboratory tests are used for diagnosis, treatment, follow-up and screening purposes. Process sigma level is one of the criteria used in the evaluation of analytical performance in clinical laboratories. The number of errors that occur in the analytical stage can be determined by process sigma levels. The actual process sigma level of a given measurement procedure is found using reference material or by comparison with reference methods. Objectives: In this study, the reference method value of AST, T.Cholesterol, LDH, Creatinine, Potassium and Sodium tests, which were studied in the Clinical Biochemistry Laboratory of KTU Medical Faculty Farabi Hospital and had reference method values in the external quality control program, examine whether the bias values obtained by three different methods according to external quality control and internal quality control are different and to compare the effects of these bias values on process sigma levels were aimed. Methods: The five-year process sigma levels of the tests included in the study were calculated according to the levels with the formula "[(TEa - Bias) / CV]". The process sigma levels were compared using the bias values calculated in three different ways according to RMV, EQC and IQC. Tests with process sigma level less than 3 were classified as unacceptable performance, between 3-3.99 borderline performance, 4-5.99 good performance, 6 and above as world class performance. Results: It was determined that the five-year mean process sigma levels calculated according to RMV were lower than the process sigma levels calculated according to EQC and IQC. In other tests except Sodium, it was observed that there was a correlation at levels of different relation between the process sigma levels calculated according to the RMV, EQC and IQC. It was determined that the process sigma levels calculated for the tests were in different categories according to different quality control materials in some months. Even when the same quality control material was used, it was observed that the process sigma levels calculated according to the months and years of the tests were in different categories. It was observed that the calculated process sigma levels for some tests performed differently according to the analytical concentration. Conclusion: It was observed that the process sigma levels of the tests varied according to the different quality control methods used. In order to evaluate the actual performance of the tests, we think that if possible, each test should be analyzed with the reference method, or the frequency of reference material usage should be increased. Because it's seen that the process sigma levels calculated for different concentrations show different performance, we think that the process sigma levels should be calculated periodically according to the levels. Key Words: Process Sigma Level, Quality Control, Analytical Performance.