In the “good old days” before automation became a way of life in the clinical laboratory, hand methods of analysis were sometimes capable of producing accurate as well as precise results-a highly gratifying situation to all concerned, especially the patient. Today in the U. S., 12,000 to 15,000 laboratories (depending upon the criteria used to define a clinical laboratory) are practicing clinical chemistry and turning out more than two billion results per year, according to a recent report from the Center for Disease Control (CDC). Somewhere in the transition from the widely used manual methods of yesterday to the extensive use of automated methods of today, accuracy as the predominant requirement for valid results was displaced by repeatability. Does one blame the engineers who adapted clinical methods to their ingenious machines in such a way as to produce highly replicable results, often at the expense of accuracy? Or does some of the fault lie with the professional clinical chemist who, under great pressure, started thinking more in terms of quantity than of quality? No matter what the historical reasons, there is little to be gained at this time in assigning blame. The goal in clinical chemistry today must be to reemphasize and recapture accuracy in analysis. At this point one may ask, “Why is accuracy in clinical chemistry necessary, anyway?” In all complex measurement systems, results, if they are to be comparable across time and distance, must be based on accuracy and not only on precision. Accuracy in measurement is related directly to the “true” value, the value that reflects reality in the most meaningful possible way. A measuring process is accurate (although not necessarily precise) if the average of a large number of replicate measurements obtained by this process is very close to the “true” value. Thus, accuracy involves traceability to the base system of units. If all practitioners agree on that base system of units, then results will be directly comparable and the bias of different methods becomes self-evident. Precision, by contrast, is only an expression of the reproducibility of a measurement system; it is not necessarily related to accuracy in any systematic way.
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