TABLE 1.

Definition of Terms

• Companion diagnostic test (CDT): A laboratory assay that provides predictive information about a patient’s response to drug therapy. This is in contrast to diagnostic or prognostic tests, which provide information about the disease process rather than response to treatment. This definition includes assays of RNA expression and allows for the potential of multiple marker tests with results interpreted by an algorithm. Assays of nonhuman analytes (e.g., viral genotype) are excluded from this definition.

• Value: A quantification of treatment outcomes (benefit vs. harm, life expectancy, quality of life) relative to health care costs.

• Value driver: A characteristic of a health care decision (test cost, drug safety, etc.) that, when modified, will substantially affect the overall value of a CDT.

• Clinical validity: The ability of a test to predict the clinical outcome of interest.17

• Clinical utility: The ability of a test to lead to improved patient outcomes when used in clinical practice.

RNA = ribonucleic acid.