Evaluation of analytical quality of coagulation parameters by sigmametric methodology

INTRODUCTION: The total testing process in the laboratory is divided into pre-analytical, analytical, and post-analytical phases. Evaluating the quality of these phases and carrying out improvement studies will increase the quality of the healthcare system. In this study, we aimed to evaluate the analytical phase of the coagulation tests using the six-sigma methodology, which is a quality management tool that aims at zero error.
METHODS: The coefficient of variation (CV%) values were calculated from the two-level internal quality control (IQC) data between January and June 2022 of the coagulation tests (prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, and D-dimer). External quality control (EQC) data were retrieved from the EQC program of external quality assurance services and used in the calculation of bias %. Total allowable error (TEa) data were obtained from the database of international organizations. The sigma value for each parameter was calculated according to the formula “(TEa%–Bias %)/ CV%.”
RESULTS: Level 1 and level 2 sigma values were calculated as 4.41 and 2.93 for PT; 5.27 and 4.31 for aPTT; 2.72 and 2.73 for fibrinogen, and 4.36 and 4.08 for D-dimer.
DISCUSSION AND CONCLUSION: Among coagulation tests in which we evaluated their analytical performances using the six sigma methodology, PT (level 2) and fibrinogen (level 1 and 2) showed poor performance (sigma value <3). We decided to follow the tests with 13s/22s/R4s/41s/8x Westgard control rules. Using these tests improvement can be achieved in the analytical process, and the overall testing process may improve by performing pre-analytical, post-analytical, and analytical assessments.