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    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 CyberLast reviewed July 25, 2026

    Definition

    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. 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 conformity assessment requires a mandatory consultation between the 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 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

    No. Only tests essential for the safe 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.
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    Primary references

    3 sources
    Link health: 2 verified 1 unchecked· last checked 2026-06-20
    EUR-Lex·1MDCG·1IMDRF·1
    1. 1
      Regulation (EU) 2017/746, Article 2(7) and Article 48(5)
      Verified
      EUR-Lexeur-lex.europa.eu
    2. 2
      MDCG 2020-16 Rev.2 Guidance on Classification
      Unchecked
      MDCGhealth.ec.europa.eu
    3. 3
      IMDRF Documents
      Verified
      IMDRFimdrf.org

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