--- title: "CDx, Companion Diagnostic (IVDR) | MedTech Terms" description: "IVD that is essential for the safe and effective use of a corresponding medicinal product to identify eligible patients or monitor treatment response." lang: en json-ld: | { "@context": "https://schema.org", "@graph": [ { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/ivdr-companion-diagnostic#term", "name": "Companion Diagnostic (IVDR)", "alternateName": "CDx", "description": "Article 2(7) of the IVDR defines a companion diagnostic as a device essential for the safe and effective use of a corresponding medicinal product to (a) identify, before or during treatment, patients most likely to benefit, or (b) identify patients likely to be at increased risk of serious adverse reactions. 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Complementary diagnostics that inform but are not required for use are not CDx." } } ] } ] } --- [ MedTech Terms The authoritative reference ](/) Browse Learn [Latest](/latest) About 1. [Home](/) 2. [Terms](/terms) 3. [Regulatory](/terms?cat=Regulatory) 4. Companion Diagnostic (IVDR) [All terms](/terms) Regulatory [Regulated Pathways](/ecosystems/regulated-pathways)[Global Markets](/ecosystems/global-markets)[Startup Lifecycle](/ecosystems/startup-lifecycle)CDx # Companion Diagnostic (IVDR) IVD that is essential for the safe and effective use of a corresponding medicinal product to identify eligible patients or monitor treatment response. Reviewed by [Christian Espinosa, Founder, Blue Goat Cyber](/authors/christian-espinosa) Last reviewed July 25, 2026 ## Definition Article 2(7) of the [IVDR](/terms/ivdr) defines a [companion diagnostic](/terms/companion-diagnostic) as a device essential for the [safe](/terms/safe-note) and effective use of a corresponding medicinal product to (a) identify, before or during treatment, patients most likely to benefit, or (b) identify patients likely to be at increased risk of serious adverse reactions. Rule 3(c) of Annex VIII classifies companion diagnostics as Class C. What the regulation says Article 48(5) and Annex IX Section 5.2 require notified bodies to seek a scientific opinion from the EMA or a national competent authority when assessing companion diagnostics linked to a centrally or nationally authorised medicinal product. ## What this means in practice [CDx](/terms/companion-diagnostic) conformity assessment requires a mandatory consultation between the [notified body](/terms/notified-body) and the EMA (or a Member State competent authority) on the suitability of the device in relation to the medicinal product. This adds meaningful lead time versus a non-CDx Class C [IVD](/terms/ivd) and requires the manufacturer to align its evidence package with the drug label. Common pitfalls - • Assuming a biomarker assay is a CDx only if the drug label names it. IVDR looks at the intended purpose claimed by the IVD manufacturer. - • Underestimating the EMA consultation timeline in project plans. - • Failing to coordinate label changes between pharma partner and IVD manufacturer, which can invalidate the CDx claim. ## Frequently asked questions Is every predictive biomarker test a companion diagnostic? No. Only tests essential for the [safe](/terms/safe-note) and effective use of a specific medicinal product meet the Article 2(7) definition. Complementary diagnostics that inform but are not required for use are not [CDx](/terms/companion-diagnostic). ## Related terms Grouped by theme ### Editor's picks · Hand-selected related concepts [ Regulatory Clinical Performance (IVDR) The ability of an IVD to yield results correlated with a clinical condition in the target population and intended user. ](/terms/ivdr-clinical-performance)[ Regulatory EU In Vitro Diagnostic Regulation(IVDR) Regulation (EU) 2017/746 governing in vitro diagnostic medical devices in the EU. ](/terms/ivdr)[ Regulatory IVDR Risk Classes A–D EU IVDR's risk-based classification: Class A (lowest) to Class D (highest). ](/terms/ivdr-classes)[ Regulatory Scientific Validity (IVDR) The association of an analyte with a clinical condition or physiological state. ](/terms/ivdr-scientific-validity) ### More in Regulatory · Same category [ Regulatory 510(k) Premarket Notification(510(k)) FDA submission demonstrating a device is substantially equivalent to a legally marketed predicate. ](/terms/510k)[ Regulatory 510(k) Summary vs 510(k) Statement Two alternative disclosure mechanisms in a 510(k) submission, a Summary is public on FDA's website; a Statement promises to share Safety & Effectiveness info on request. ](/terms/510k-summary-vs-statement)[ Regulatory 513(g) Request for Information(513(g)) Formal mechanism to ask FDA whether a product is a device and, if so, its likely classification. ](/terms/513g)[ Regulatory Abbreviated 510(k) 510(k) variant that relies on FDA guidance, special controls, or recognized consensus standards. ](/terms/abbreviated-510k) Cited by Where this term appears across MedTech Terms. Ecosystems (3) - [Regulated Pathways](/ecosystems/regulated-pathways) - [Global Markets](/ecosystems/global-markets) - [Startup Lifecycle](/ecosystems/startup-lifecycle) ## Primary references 3 sources Link health: 2 verified 1 unchecked · last checked 2026-06-20 EUR-Lex· 1 MDCG· 1 IMDRF· 1 1. [1 Regulation (EU) 2017/746, Article 2(7) and Article 48(5) Verified EUR-Lex eur-lex.europa.eu ](https://eur-lex.europa.eu/eli/reg/2017/746/oj) 2. [2 MDCG 2020-16 Rev.2 Guidance on Classification Unchecked MDCG health.ec.europa.eu ](https://health.ec.europa.eu/document/download/6b5cb2c4-19a0-4a54-9df4-d8b1d6b3f4c1_en) 3. [3 IMDRF Documents Verified IMDRF imdrf.org ](https://www.imdrf.org/documents) Inline markers like \[1\] jump to the matching reference above. Sponsor note ### Navigating an FDA or EU MDR submission? Blue Goat Cyber supports the cybersecurity content of premarket submissions, from threat models to the 524B narrative. [Book a 30-minute discovery session](https://go.bluegoatcyber.com/meetings/blue-goat-cyber/discovery-session) - No obligation - Expert-led from minute one - NDA available on request MedTech Terms is a community resource sponsored by [Blue Goat Cyber](https://bluegoatcyber.com). Definitions are independent of any vendor. On this term Category Regulatory Acronym CDx Sources 3 Updated 7/25/2026 [Compare with another term](/compare?a=ivdr-companion-diagnostic) Learn in 60 seconds Card Lesson Quiz IVD that is essential for the safe and effective use of a corresponding medicinal product to identify eligible patients or monitor treatment response. - · This adds meaningful lead time versus a non-CDx Class C IVD and requires the manufacturer to align its evidence package with the drug label. - · Rule 3(c) of Annex VIII classifies companion diagnostics as Class C. Remember this Watch out: Assuming a biomarker assay is a CDx only if the drug label names it. IVDR looks at the intended purpose claimed by the IVD manufacturer. Related terms - [EU In Vitro Diagnostic Regulation(IVDR) ](/terms/ivdr) - [IVDR Risk Classes A–D ](/terms/ivdr-classes) - [Clinical Performance (IVDR) ](/terms/ivdr-clinical-performance) - [Scientific Validity (IVDR) ](/terms/ivdr-scientific-validity) You may also need Auto-suggested from Regulatory and shared keywords. - [Performance Study Application (IVDR) ](/terms/ivdr-performance-study-application) - [Post-Market Surveillance Plan (IVDR) ](/terms/ivdr-pms-plan) - [Companion Diagnostic(CDx) ](/terms/companion-diagnostic) - [Performance Study (IVDR) ](/terms/ivdr-performance-study) - [Class D Batch Verification (IVDR) ](/terms/ivdr-class-d-batch-verification) - [Fundamental Rights Impact Assessment(FRIA) ](/terms/ai-act-fria) [All Regulatory terms](/terms?cat=Regulatory) From the Blue Goat network Related resources and services on this topic. - [ MedTech Cybersecurity Standards Authoritative reference for the standards and guidances behind medical device cybersecurity. ](https://medtechcyberstandards.com) - [ MedTech Cybersecurity Crosswalk International crosswalk of medical device cybersecurity requirements across regulators. ](https://mdccrosswalk.com) - [ MedTech Truths Common misconceptions about medical device development - debunked. ](https://mdcmisconceptions.com) - [ MedTech Launchpad MedTech funding rounds, accelerators, and launch resources. ](https://medtechlaunchguide.com) MedTech Terms An authoritative, plain-language reference for the regulatory, quality, cybersecurity, and software terms that shape modern medical devices. 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