Test selections are based on subjective clinical judgment, evaluation of risks and benefits, guidelines and recommendations (refer to Table 1.2), and evidence-based healthcare.

Evidence-based guidelines grade the quality of scientific evidence for a specific test or procedure based on published reports of clinical trials, expert consensus, or clinical expertise. Levels of evidence are A, B, C, and E, with A indicating that a test or procedure is supported by the best scientific evidence and E referring to expert opinion or consensus (Chart 1.1).

Use of these guidelines for selecting or eliminating diagnostic tests may aid in effective case management and cost containment. Selecting tests based on evidence-based guidelines can overcome “blanket testing”—in which the provider orders unwarranted tests, often in response to pressure from patients—which has resulted in significant costs to the healthcare system. It can also identify when multiplex testing (conducting multiple tests on a single sample) can be beneficial, such as with autoimmune disorders or genetically inherited disease, producing cost savings in the long run.