Clinical Laboratory Tests: Which, Why, and What Do The Results Mean?
Frank H. Wians



According to Dr. Michael Laposata, the medical specialty that nearly every practicing physician relies on every day, for which training in many medical schools is limited to no more than a scattered few lectures throughout the entire curriculum, is “laboratory medicine.” The importance of understanding the principles for selecting and ordering the most rational laboratory test(s) on a specific patient is heightened in the current age of managed care, medical necessity, and outcome-oriented medicine. The days of a “shotgun approach” to ordering laboratory tests has, of necessity, been replaced by a “rifle” (or targeted) approach based on an understanding of the test’s diagnostic performance and the major “legitimate” reasons for ordering a laboratory test. Such an understanding is critical to good laboratory practice and patient outcomes.

The purpose of this CE Update is to discuss the laboratory testing cycle and its importance in diagnostic decision making. This discussion will begin with some general comments about approaches to ordering clinical laboratory tests, followed by “real-world” examples to illustrate these approaches. We will then review the important diagnostic performance characteristics of laboratory tests, how they are calculated, and a principal tool (ie, receiver-operator characteristic [ROC] curves) used to assess the diagnostic accuracy of a laboratory test at specific cutoff values for the test. We will then discuss how laboratory tests are interpreted using a reference interval and its limitations, followed by some brief remarks about the concepts critical difference and neural network.

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