Companion diagnostic

A companion diagnostic (CDx) is a diagnostic test used as a companion to a therapeutic drug to determine its applicability to a specific person. A companion diagnostic (CDx) is a diagnostic test used as a companion to a therapeutic drug to determine its applicability to a specific person. Companion diagnostics are co-developed with drugs to aid in selecting or excluding patient groups for treatment with that particular drug on the basis of their biological characteristics that determine responders and non-responders to the therapy. Companion diagnostics are developed based on companion biomarkers, biomarkers that prospectively help predict likely response or severe toxicity.