Three-pool analysis for quality control: a method for daily differentiation of analytic error from random variability.

Using the Z statistic we have devised a novel, mathematically simple concept for daily quality control of laboratory procedures. The method allows rapid identification and differentiation of systematic errors from random variability on a daily basis, increases confidence in the accuracy of reported results, reduces the number of repeat analyses, and allows the analyst to detect a deteriorating quality control pool. Using three controls instead of one or two increases the chance of detecting out-of-control situations and uses simplified statistical calculations summarized on a single graphic wall chart to monitor the daily accuracy and precision of analytic procedures. The method is adaptable to any type of specimen quantitatively analyzed and can be used in large or small laboratories with light or heavy workloads. This paper reflects what happens in a small laboratory with only one run each day, but, the system has been tested in a large community hospital with a heavy workload and multiple runs each day. Although this procedure is presented for the clinical laboratory, the method would be equally useful in industry.