INITIAL APPLICATION OF SIX SIGMA IN QUALITY CONTROL OF SELECTED COAGULATION TESTS AT THE NATIONAL INSTITUTE OF HEMATOLOGY AND BLOOD TRANSFUSION
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Abstract
Objective: To characterize analytical performance using Six Sigma metrics and propose appropriate quality-control rules and internal quality-control (IQC) frequencies for prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen assays performed on the STA-R Max system.
Materials and methods: This descriptive study used two-level IQC data and RIQAS external quality-assessment results collected from April to September 2024 at the Hemostasis Department, National Institute of Hematology and Blood Transfusion. Monthly CVs were derived from IQC data, and the six-month weighted mean CV was calculated using the number of IQC measurements in each month as weights. Bias was derived from external quality assessment, and Sigma was calculated as (TEa - |bias|)/CV. The allowable total error (TEa) was 15% for PT, 15% for APTT, and 20% for fibrinogen. The quality goal index (QGI) was used to identify priority areas for assays with Sigma below 6.
Results: Six-month weighted mean CVs at the normal/abnormal control levels were 1.9%/2.7% for PT, 2.0%/2.2% for APTT, and 2.0%/2.5% for fibrinogen. Mean biases were 4.0%, 4.3%, and 3.4%, respectively; all external quality-assessment results had absolute SDI values below 2. Sigma values at the normal/abnormal levels were 5.8/4.1 for PT, 5.4/4.7 for APTT, and 8.3/6.6 for fibrinogen. Based on the poorer-performing level of each assay, PT and APTT require the 1₃s/2₂s/R₄s/4₁s multirule with an IQC interval of no more than 200 patient samples, whereas fibrinogen may use the 1₃s rule with an interval of no more than 1,000 samples.
Conclusion: Six Sigma metrics quantify assay-specific performance and support risk-based IQC planning. Fibrinogen showed the best performance, whereas PT and APTT at the abnormal control level require more stringent control and improved trueness.
Keywords
Six Sigma, coagulation tests, internal quality control, Westgard rules, STA-R Max
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References
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