October 14, 2026

Companion Diagnostics (CDx) play an increasingly important role in precision medicine by helping identify patients who may be eligible for a particular therapeutic product or who may require specific treatment decisions.

Because CDx products can directly influence treatment selection, regulatory requirements may involve a close relationship between the diagnostic, the associated medicinal product, clinical evidence, analytical performance, and labeling.

For pharmaceutical companies, biotechnology organizations, diagnostic manufacturers, laboratories, and developers of precision-medicine technologies, an integrated regulatory strategy is essential.

Maven Regulatory Solutions provides CDx Regulatory Affairs Consulting covering regulatory strategy, classification, clinical evidence, analytical validation, submission planning, regulatory interactions, registration and lifecycle management across the United States, European Union and United Kingdom.

What Is a Companion Diagnostic?

A Companion Diagnostic is an in vitro diagnostic device used to provide information that is essential for the safe and effective use of a corresponding medicinal product.

Depending on the therapeutic context, a CDx may help identify:

  • Patients are likely to benefit from therapy
  • Patients at increased risk of serious adverse reactions
  • Patients requiring a particular treatment strategy
  • Biomarker-positive patient populations
  • Molecular or genetic characteristics relevant to treatment

CDx development therefore requires coordination between diagnostic development and pharmaceutical development.

The regulatory pathway can involve:

Biomarker strategy → Assay development → Analytical validation → Clinical evidence → Regulatory strategy → Diagnostic submission → Drug/biologic alignment → Market authorization → Lifecycle management

Why CDx Regulatory Strategy Is Different

Unlike many conventional IVDs, CDx products may be directly connected to the use of a medicinal product.

This means regulatory planning may need to address both:

Diagnostic requirements + Therapeutic-product requirements

Key considerations may include:

  • Biomarker selection
  • Intended use
  • Patient population
  • Assay performance
  • Cut-off determination
  • Clinical trial strategy
  • Specimen requirements
  • Companion therapeutic relationship
  • Labeling alignment
  • Regulatory submission timing
  • Post-market changes

Maven helps organizations develop an integrated regulatory roadmap for these requirements.

CDx Regulatory Pathway — United States

In the United States, CDx products are regulated by the FDA's Center for Devices and Radiological Health (CDRH), while the associated therapeutic product may be reviewed through the applicable FDA drug or biologic center.

The appropriate diagnostic pathway depends on the characteristics and risk profile of the CDx.

Potential pathways can include:

1. 510(k)

A 510(k) may be appropriate where the device can demonstrate substantial equivalence to a legally marketed predicate.

2. De Novo

A De Novo pathway may be relevant for certain novel, moderate-risk diagnostic devices without an appropriate predicate.

3. PMA

Higher-risk CDx products may require PMA review supported by appropriate evidence demonstrating reasonable assurance of safety and effectiveness.

FDA pre-submission

Early FDA interaction can help clarify regulatory expectations, clinical evidence requirements, analytical studies and submission strategy.

Maven can support:

  • CDx regulatory pathway assessment
  • FDA classification
  • Pre-submission strategy
  • 510(k) planning
  • De Novo strategy
  • PMA strategy
  • Clinical trial strategy
  • Analytical validation planning
  • Clinical performance strategy
  • FDA submission preparation
  • Deficiency response
  • Labeling alignment
  • Drug-device regulatory coordination

CDx Regulatory Pathway — European Union

The EU regulatory framework for IVDs is governed by Regulation (EU) 2017/746 (IVDR).

CDx products generally require careful assessment under the IVDR classification and conformity assessment framework.

The regulatory strategy should consider:

  • Intended purpose
  • Biomarker
  • Patient population
  • Therapeutic relationship
  • Risk classification
  • Performance evaluation
  • Clinical evidence
  • Technical documentation
  • Notified Body involvement
  • CE marking
  • Post-market surveillance

For CDx products associated with medicinal products, coordination between diagnostic and pharmaceutical regulatory strategies is particularly important.

EU CDx Regulatory Services

Maven supports:

  • IVDR classification
  • CDx regulatory strategy
  • Intended-purpose review
  • Performance evaluation planning
  • Analytical performance assessment
  • Clinical performance strategy
  • Technical documentation
  • Clinical evidence strategy
  • Notified Body interaction
  • CE marking support
  • Labeling review
  • PMS and PMPF planning
  • Regulatory change assessment
  • Lifecycle management

CDx Regulatory Pathway — United Kingdom

CDx products entering the UK require assessment against the applicable UK medical-device regulatory framework.

Regulatory planning may involve:

  • Product classification
  • Conformity assessment
  • Technical documentation
  • UK Responsible Person requirements
  • MHRA registration
  • Labeling
  • Clinical and performance evidence
  • Post-market surveillance

For CDx products associated with medicine, regulatory planning should also consider the relationship between diagnostic and therapeutic products.

Maven supports UK CDx regulatory activities including:

  • MHRA strategy
  • Product classification
  • UK registration
  • Conformity assessment
  • Technical documentation
  • Performance evaluation
  • Clinical evidence
  • Labeling
  • Post-market surveillance
  • Regulatory lifecycle management

CDx Analytical Performance Validation

Analytical validation is a critical component of CDx development.

Depending on the essay, performance characteristics can include:

  • Accuracy
  • Precision
  • Reproducibility
  • Analytical sensitivity
  • Analytical specificity
  • Limit of detection
  • Limit of quantification
  • Interference
  • Cross-reactivity
  • Specimen stability
  • Cut-off determination
  • Lot-to-lot consistency

The analytical validation strategy should be aligned with the intended clinical application and regulatory claims.

CDx Clinical Evidence Strategy

Clinical evidence is particularly important because CDx results may affect therapeutic decisions.

A CDx clinical strategy may need to be addressed:

Patient population → Specimen type → Biomarker → Assay → Cut-off → Treatment → Clinical outcome

Maven can help organizations assess clinical evidence requirements and develop regulatory strategies aligned with the intended use of the CDx.

CDx and Pharmaceutical Development

One of the most important considerations in companion diagnostic development is coordination between the diagnostic and therapeutic development programs.

Regulatory planning may need to be addressed:

  • Biomarker strategy
  • Patient-selection strategy
  • Clinical trial design
  • Assay availability during clinical development
  • Diagnostic bridging
  • Assay changes
  • Therapeutic labeling
  • Diagnostic labeling
  • Regulatory submission timing
  • Post-approval changes

An integrated approach can help minimize inconsistencies between diagnostic and therapeutic regulatory submissions.

CDx Technical Documentation

CDx technical documentation may include:

  • Device description
  • Intended purpose
  • Classification rationale
  • Risk management
  • Analytical performance
  • Clinical performance
  • Performance evaluation
  • Manufacturing information
  • Software documentation
  • Stability
  • Labeling
  • Instructions for use
  • PMS documentation
  • Vigilance procedures
  • Regulatory correspondence

Maven provides technical-documentation review and gap assessments to support submission readiness.

CDx Regulatory Services Across the Product Lifecycle

1. Biomarker & Intended-Purpose Assessment

Evaluate the proposed diagnostic use and therapeutic relationship.

2. Regulatory Classification

Determine the applicable regulatory classification and pathway.

3. Regulatory Strategy

Develop country-specific regulatory roadmaps.

4. Clinical & Analytical Strategy

Align evidence requirements with intended use and regulatory expectations.

5. Submission Preparation

Support regulatory documentation and submission packages.

6. Regulatory Authority Interaction

Support responses to questions and regulatory requests.

7. Labeling Alignment

Review diagnostic and therapeutic labeling consistency.

8. Market Registration

Support applicable registration and market-access requirements.

9. Lifecycle Management

Support modifications, regulatory changes, PMS and post-market requirements.

FAQs

1. What is a CDx?

A companion diagnostic is an IVD used to provide essential information for the safe and effective use of a corresponding medicinal product.

2. Are CDx products regulated as IVDs?

Generally, CDx products fall within IVD regulatory frameworks, but the precise regulatory pathway depends on the jurisdiction, product characteristics and intended purpose.

3. What regulatory pathway does a US CDx require?

Depending on risk and regulatory characteristics, a US CDx may potentially follow a 510(k), De Novo or PMA pathway, among other applicable regulatory mechanisms.

4. What regulation applies to CDx products in the EU?

EU CDx products are regulated under the IVDR framework, Regulation (EU) 2017/746, with classification and conformity assessment requirements determined by the device and intended purpose.

5. Does CDx development need to be coordinated with drug development?

Yes. Because a CDx can determine patient selection or treatment decisions, diagnostic and therapeutic development programs may need to be strategically coordinated.

6. Can Maven support CDx registration in the US, UK and EU?

Maven Regulatory Solutions provides regulatory strategy, documentation, clinical and analytical evidence planning, submission support and lifecycle regulatory services for CDx programs across major markets.

How Maven Regulatory Solutions Can Help

Maven Regulatory Solutions supports pharmaceutical, biotechnology, diagnostic and medical-device organizations with global CDx regulatory strategy and compliance.

Our services include:

  • CDx Regulatory Strategy
  • US FDA CDx Consulting
  • 510(k) Strategy
  • De Novo Regulatory Support
  • PMA Strategy
  • EU IVDR CDx Consulting
  • UK MHRA Regulatory Support
  • CDx Classification
  • Biomarker Regulatory Strategy
  • Analytical Validation Strategy
  • Clinical Evidence Planning
  • Performance Evaluation
  • Technical Documentation
  • Regulatory Submission Support
  • Labeling & Claims Review
  • Notified Body Support
  • Drug–Diagnostic Regulatory Alignment
  • Post-Market Surveillance
  • Lifecycle Management
  • Regulatory Intelligence

Maven Regulatory Solutions — Science. Compliance. Impact.