Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · EU in vitro diagnostics: IVDR

Companion diagnostic (IVDR)

Also known as: CDx, Companion diagnostic device

Under the EU In Vitro Diagnostic Medical Devices Regulation (EU) 2017/746, a companion diagnostic is a device that is essential for the safe and effective use of a corresponding medicinal product, to identify, before or during treatment, patients who are most likely to benefit from it or who are likely to be at increased risk of serious adverse reactions. Companion diagnostics are class C, and the notified body must consult the European Medicines Agency or a national medicines authority on the device’s suitability for use with the medicinal product.

  • EU
  • IVDR
  • Pharma

In one sentence

A companion diagnostic (IVDR Art. 2(7)) is a class C test essential for a medicine’s safe and effective use; the notified body consults a medicines authority.

Example

A diagnostics company develops a tumor mutation test alongside a targeted cancer drug. The notified body reviews the test under the IVDR and consults the EMA, since the drug is centrally authorized, before issuing the certificate.

How it applies

  • Classification: Companion diagnostics are class C under Rule 3 of Annex VIII; see Device classification (IVDR).
  • Medicines authority consultation: Before certifying, the notified body seeks a scientific opinion from the EMA or a national medicines authority on whether the device is suitable for use with the medicinal product. Changes affecting that suitability trigger a further consultation.
  • Co-development: Evidence for the test often comes from the drug’s clinical trials. Samples, assay versions and cut-offs used in the trials have to be traceable to the commercial device.
  • Performance studies: Companion diagnostic performance studies follow the IVDR application route, with exceptions for studies using only leftover samples.
  • Laboratory tests: Health institutions may use their own companion diagnostic tests under the in-house exemption if its conditions are met.
  • Technical documentation: The intended purpose names the medicinal product or product class. IFU, performance evaluation report and the medicine’s product information must describe the same biomarker, specimen type and cut-off.

Companion diagnostic vs. drug-device combination

A companion diagnostic is a separate IVD that selects patients for a medicine; it is regulated under the IVDR even when developed together with the drug. A drug-device combination delivers or contains the medicine and falls under medicinal product law or the MDR. The two can coexist for one therapy but follow different routes.

Compared with the USA

The FDA regulates in vitro companion diagnostics as devices, usually through premarket approval, and coordinates their review with the review of the corresponding drug. Its approach is described in its 2014 guidance on in vitro companion diagnostic devices.