A Two-Tier Patient-Based Real-Time Quality Control Program Integrating K-Means Department Stratification and Inter-Instrument Ratios Improves Detection of Small Systematic Errors in Creatinine Testing

Abstract

Background/Objectives: Patient-based real-time quality control (PBRTQC) complements traditional internal quality control. This study validates a ratio-based PBRTQC integrating department clustering with inter-instrument ratio monitoring. Methods: Creatinine data (384,730 cases, 2025) from three measuring systems (A, B, C) were analyzed; conventional PBRTQC on unstratified Instrument A data served as comparator. Departments were stratified by K-means clustering of annual mean/SD, keeping the low-mean cluster (124 departments). The data of each measuring system were split chronologically: first-layer PBRTQC was trained on the first part, the second trained the ratio programs, and the third provided independent validation. Three systematic errors (fixed additive offsets of +5.28 and +10.56 μmol/L, and a progressive offset rising to +10.56 μmol/L, corresponding to 6% and 12% of the first-layer action limit) were simulated to assess the true positive rate (TPR), false positive rate (FPR), median samples to detection (MNPed), detection time and diagnostic odds ratio (DOR). Results: Under the fixed +5.28 μmol/L (6%) offset, A-B TPR was 28.83% versus 6.77% for traditional PBRTQC, with MNPed reduced from 34 to 20. Under the progressive offset rising to +10.56 μmol/L (12%), A-B TPR was 29.00% versus 8.35%, and detection time fell from 20 to 14 min. Under the fixed +10.56 μmol/L (12%) offset, A–B and A–C TPR reached 70.15% and 74.72% (MNPed 8 and 5; detection time 2 and 1 min). Across all scenarios the ratio programs achieved higher DOR. A stratified single-instrument comparator showed complementary contributions of stratification and ratio monitoring (TPR at the +5.28 μmol/L offset: 6.77%, 15.61% and 28.83%). Conclusions: Integrating department stratification with ratio-based PBRTQC markedly improves detection of small systematic errors in creatinine testing, albeit with more false positives, offering a transferable framework for laboratories using multiple same-platform measuring systems.