OBJECTIVES: Irregular fluctuations in patient data affect patient-based real-time quality control (PBRTQC) performance. Moreover, results among multiple instruments can be inconsistent. Here, we explored a simple index, double-module ratio, to improve PBRTQC performance through overcoming irregular fluctuations, and ensure consistency across multiple instruments in real time. METHODS: Laboratory results from the same departments tested centrally such that the original patient data fluctuated irregularly during the day were included. Albumin (Alb), calcium (Ca), cholinesterase (ChE), and total protein (TP) indexes derived from a single module were processed through conventional PBRTQC. The ratios calculated from PBRTQC data of two modules were defined as double-module ratios (R RESULTS: All four ratios (R CONCLUSIONS: As a PBRTQC index, double-module ratios can facilitate small shift detection and ensure result consistency among various modules in real time.