Practical Quality Control: the Experiences of a Public Health Laboratory

In the 1930’s W.A. Shewhart pioneered the application of statistical principles to the quality control (QC) of production processes, eventually publishing the landmark book “Economic Control of Quality of Manufactured Products” (Shewhart, 1931). In this book, he states that a phenomenon is under control if its future variation can be predicted (within limits) based on previous experience. This is precisely the idea behind the control charts used in measurement processes—specifically, for chemical analysis. The International Organization for Standardization (ISO), in its standard ISO 9000 (ISO, 2005a), defines quality control as “the part of quality management focused on fulfilling quality requirements”. According to the standard, quality management also includes quality planning, quality assurance and quality improvement. The above definition is rather vague, because quality management systems based on the ISO 9000 family of standards can be applied to any kind of organization regardless of its field of activity, its size or whether it is from the public or private sectors. Testing laboratories typically distinguish between internal and external QC. In this context, the International Union of Pure and Applied Chemistry (IUPAC, 1998) gives a definition of internal QC that is well-suited to an analytical laboratory: “the set of procedures undertaken by laboratory staff for the continuous monitoring of operation and the results of measurements in order to decide whether results are reliable enough to be released”. Although the aforementioned document does not formally define external QC, it does mention that external control may be done by submitting blind samples to the measuring laboratory. This activity can be organized in the form of a collaborative test..