FDA Companion Diagnostics: A Complete Regulatory Guide to CDx Development, Approval, and Co-Development Strategy

The FDA companion diagnostic (CDx) regulatory framework is one of the most complex intersections in MedTech: a single device that must satisfy the standards of two regulators (CDRH and CDER or CBER), coordinate with a pharmaceutical development timeline measured in years, and carry clinical consequences that make a wrong result directly harmful to patients.

A misaligned CDx strategy does not just delays the diagnostic. It delays the drug.

In tissue-agnostic oncology indications, the mean gap between drug approval and the corresponding CDx approval has historically approached two years. That is not a regulatory abstraction, those are patients waiting for access to an already-approved therapy because the diagnostic program was not adequately integrated from the outset.

This guide covers the complete FDA CDx regulatory pathway: what a companion diagnostic is under US law, how PMA and the modular submission process works in practice, how Q-submissions and pre-sub meetings should be structured, how FDA’s November 2025 proposed reclassification of NGS and NAAT-based oncology CDx from Class III to Class II will affect program planning, and what a realistic co-development timeline looks like when both a drug and a diagnostic are advancing in parallel.

What Is an FDA Companion Diagnostic? The Legal Definition and Its Practical Consequences

FDA’s 2014 final guidance on In Vitro Companion Diagnostic Devices established the foundational definition that governs every CDx program in the United States. An IVD companion diagnostic device provides information that is essential for the safe and effective use of a corresponding therapeutic product.

The word essential is not rhetorical. When FDA determines that a diagnostic result is necessary for any of the following functions, both the drug label and the device label must reflect that requirement:

• Patient selection: identifying patients most likely to benefit from the therapy
• Safety exclusion: identifying patients at elevated risk for serious adverse reactions
• Dose optimisation: monitoring therapeutic or toxic effects to guide dose adjustment
• Response monitoring: tracking treatment response after initiation

The applicable labeling regulations are 21 CFR 201.57 for therapeutic product labeling and 21 CFR 809.10 for IVD device labeling. Both labels must be aligned at time of approval. That requirement is the single most consequential structural feature of CDx regulation, and the one most often underestimated by sponsors approaching their first combined program.

The greatest value of experienced CDx support lies in anticipating cross-functional and regulatory risks early. Sponsors frequently overestimate their ability to manage these interfaces internally, particularly if they have limited prior experience with end-to-end companion diagnostic approvals. Intended use definition, analytical validation planning, clinical sample strategy, and regulatory positioning are highly interdependent, changes to one element consistently have material implications for the others.

Callum Pickett, Clinical Alliance Lead, MDx CRO

CDx vs. CDMO: An Important Distinction

Before addressing regulatory pathway, it is worth clarifying a distinction that frequently causes confusion in early-stage programs. A CDx development partner (such as a CRO with IVD regulatory expertise) is engaged to define what the diagnostic should be, guide R&D, manage analytical and clinical validation, ensure IVDR and FDA regulatory compliance throughout the development lifecycle, and advise on pathway strategy. A Contract Development and Manufacturing Organisation (CDMO) is engaged to manufacture a device that has already been defined. The CDMO can only produce what has already been designed and validated; it cannot assume responsibility for the regulatory fate of the product. Sponsors who engage a CDMO without first engaging a CDx development partner often discover, late in development, that their device lacks the analytical validation infrastructure or regulatory documentation to support an FDA submission.

How FDA Reviews a Companion Diagnostic: CDRH, CDER, and CBER Working in Parallel

Every IVD companion diagnostic program in the United States touches three FDA centres simultaneously. Regulatory affairs teams that approach CDx review as a single-centre process routinely encounter the coordination gap at the worst possible moment: during submission review.

FDA Centre	Full Name	Primary CDx Responsibility
CDRH	Center for Devices and Radiological Health	Reviews and approves the IVD companion diagnostic device; receives all PMA, Q-Submission, and IDE filings
CDER	Center for Drug Evaluation and Research	Reviews the NDA or BLA for associated small-molecule drugs; manages the IND; owns the therapeutic product label
CBER	Center for Biologics Evaluation and Research	Reviews biologics including monoclonal antibodies and gene therapies; handles HLA assays and certain blood-compatibility diagnostics

Two parallel submission tracks with different evidentiary standards, different review timelines, and different internal review divisions that must coordinate with each other. FDA’s codevelopment guidance makes clear that separate marketing applications are always required for the therapeutic product and the IVD companion diagnostic, even when a single sponsor is developing both.

Letters of Authorization allow each application to cross-reference the other’s proprietary data without duplicating confidential submissions. Setting up these agreements early, before either programme is well advanced, is a structural requirement, not a convenience.

Practical Implication

FDA strongly encourages sponsors to request early joint meetings involving all relevant centres before an IND is filed. Teams that wait until the NDA or BLA stage to engage CDRH consistently face longer review timelines and a higher volume of deficiency letters. The cost of a late start to FDA dialogue is not merely a delay, it is rework at a stage when rework is most expensive.

The PMA Pathway: How Premarket Approval Actually Works for a CDx

Premarket Approval under section 515 of the FD&C Act is the predominant regulatory route for companion diagnostics in the United States. FDA classifies most companion diagnostics as Class III devices on the basis that a misclassified result directly influences whether a patient receives or is withheld from a targeted therapy. Of the more than 80 drug-CDx combinations approved through early 2025, the overwhelming majority obtained marketing authorisation through the PMA pathway.

What a PMA Submission Must Contain

A PMA submission must demonstrate reasonable assurance of safety and effectiveness. FDA has expressed a consistent preference for the modular PMA format, in which sponsors submit four sequential modules as data become available rather than waiting for a complete package.

Module	Content
Module 1	Device description and manufacturing information
Module 2	Non-clinical performance studies (analytical validation)
Module 3	Clinical studies and bridging data
Module 4	Proposed labeling

Engaging CDRH through a Pre-Submission (Q-Submission) before filing Module 1 is considered standard practice. That Pre-Submission should align the table of contents, content expectations for each module, and review timelines. Sponsors who skip this step and file directly tend to receive Module 1 deficiency letters that delay the entire sequence.

What the PMA Pathway Costs in Time and Fees

The PMA pathway is resource-intensive. User fees run into the hundreds of thousands of dollars. The statutory review clock is 180 days from acceptance under normal circumstances. Advisory panel meetings may be convened for novel device types or complex clinical performance questions, which can extend that timeline.

The modular format reduces total elapsed time by allowing CDRH to begin reviewing manufacturing and analytical data while clinical evidence is still being generated. However, the modular approach requires that Module 1, which includes the full device description and intended use, is sufficiently precise. Intended use ambiguity at the Module 1 stage tends to propagate into deficiencies across every subsequent module.

As Callum Explains, the earliest PMA modules should prioritise intended use definition, device architecture, analytical validation strategy, and clinical evidence planning. Intended use is the highest priority because it drives analytical requirements, specimen strategy, clinical study design, and labelling. Sponsors often attempt to preserve flexibility through broad or provisional language, but CDRH generally expects specificity. Ambiguity at this stage leads to downstream revisions and delays. The most common CDRH deficiencies relate to insufficiently precise intended use language, underdeveloped bridging strategies, weak cut-off justification, incomplete software documentation, and inadequate reconciliation of assay changes across modules.

When a Supplemental PMA (sPMA) Is the Right Mechanism

For a drug sponsor adding a companion diagnostic indication to an already-approved PMA device, the correct filing mechanism is a Supplemental PMA. The sPMA is a narrower submission focused on the analytical and clinical validation data supporting the specific new drug indication. It does not require re-justifying the device’s general safety profile, which substantially reduces the evidentiary package. This pathway is frequently used as the CDx landscape matures and new therapeutic indications are added to existing cleared platforms.

Q-Submissions and Pre-Sub Meetings: How to Use FDA’s Feedback Programme Effectively

A Pre-Submission under the FDA’s Q-Submission Programme is not optional for most novel or higher-risk CDx programmes, it is the mechanism by which sponsors and CDRH align on regulatory expectations before significant evidence generation has begun. Done well, a Pre-Submission meeting eliminates a class of avoidable deficiencies and establishes a shared framework for the entire submission strategy.

When to Submit a Pre-Submission

The first Pre-Submission interaction with FDA should occur once the following are reasonably defined: intended use statement, assay platform, specimen strategy, analytical validation concept, and clinical trial integration model.

Engaging too late with the FDA creates a risk of regulatory work being wasted. If a diagnostic partner is committed to the PMA route but FDA discussion suggests the 510(k) route, the organisation has over-invested in a more rigorous strategy than needed. Conversely, if they have embarked on a 510(k) strategy and FDA recommends PMA, they run the risk of having insufficient analytical and clinical evidence. Depending on how far into development the diagnostic partner is, unexpected requirements for additional studies can push back FDA submission and marketing by months to years.

Callum Pickett, Clinical Alliance Lead, MDx CRO

What to Cover in a CDx Pre-Submission Meeting

The questions posed to FDA should be specific and decision-oriented. A Pre-Submission is most effective when it provides sufficient background and preliminary data for CDRH to comment on a defined regulatory question rather than on the development programme in general. Topics should address:

• Proposed regulatory pathway (PMA, 510(k), or De Novo) and rationale
• Device description and intended use wording, the precise language FDA will accept
• Investigational-use strategy and IDE status determination
• Analytical validation pla, which studies FDA expects and in what format
• Clinical validation plan, how clinical performance will be demonstrated
• Assay lock-down and bridging approach, the most scrutinised area in CDx submissions
• Labelling strategy and alignment with therapeutic product label
• Coordination with therapeutic development timelines

Pre-IDE Q-Submissions

For programmes where an IDE may be required, a Pre-IDE Q-Submission allows for feedback from CDRH on approximately three to four topics prior to filing the IDE itself. The Pre-IDE ideally includes draft protocols or detailed summaries of proposed study designs. This step is particularly recommended when the significant risk determination is genuinely uncertain, FDA will provide a written position that prevents subsequent disagreement over IDE applicability.

Investigational Device Exemption (IDE): Significant Risk vs. Non-Significant Risk

When a CDx is used in a therapeutic clinical trial, particularly when the assay result influences patient enrolment, treatment assignment, or a clinical management decision, the sponsor must determine whether the study device is a significant risk (SR) or non-significant risk (NSR) device under 21 CFR 812.3(m).

This determination has material procedural consequences:

Risk Designation	Requirement	Consequence
Significant Risk (SR)	IDE application to FDA + IRB approval	Study cannot begin until both FDA and IRB approve. 30-day FDA review clock. IDE content requirements under 21 CFR 812.20(b).
Non-Significant Risk (NSR)	IRB approval only	Abbreviated requirements under 21 CFR 812.2(b). No IDE submission to FDA required.

The significant risk determination must answer four key questions drawn from FDA’s draft guidance on Investigational IVDs Used in Clinical Investigations of Drug and Biological Products (2024):

1. Will use of the IVD results lead subjects to forego or delay a treatment known to be effective?
2. Will IVD results expose subjects to safety risks exceeding those in the control arm?
3. Based on existing biomarker evidence, would incorrect IVD results present a serious risk to subjects?
4. Does the IVD require invasive sampling not part of standard care?

Sponsors are responsible for presenting the initial determination to the IRB. FDA and the IRB will review the assessment and may disagree with the sponsor’s position. If the IRB and FDA reach a different conclusion, the sponsor may appeal.

Important

For CDx devices used in oncology trials where the assay result determines treatment eligibility, a significant risk determination is generally expected. The consequential question is not whether IDE applies but how to structure the IDE submission and coordination between CDRH and the drug review centre.

FDA’s November 2025 Proposed Reclassification: What It Means for NGS and NAAT-Based Oncology CDx

In November 2025, FDA published a proposed order in the Federal Register that would materially change the submission pathway for a major category of companion diagnostics. Docketed as FDA-2025-N-4622, the proposed rule would create a new Class II device type under 21 CFR 866.6075. If finalised, NGS panels, PCR-based assays, and NAAT-based oncology companion diagnostics would move from the Class III PMA pathway to 510(k) clearance with defined special controls.

The Regulatory Logic Behind the Proposed Reclassification

FDA’s rationale is grounded in retrospective analysis of oncology CDx approvals over the past decade. The agency concluded that the risk profile of nucleic acid-based oncology tests is now sufficiently characterisable through defined special controls covering:

• Analytical validity requirements (accuracy, precision, limit of detection, reportable range)
• Clinical validity expectations linking the biomarker to the therapeutic indication
• Design and labelling specifications consistent with the corresponding drug label
• Post-market controls

The evidentiary bar remains rigorous. What changes is the submission architecture: substantial equivalence to a well-characterised archetype would, in principle, eliminate the need for a full clinical trial per new test when analytical comparability can be demonstrated.

What This Reclassification Does Not Cover

This proposed reclassification applies exclusively to nucleic acid-based oncology tests. IHC-based, FISH-based, imaging-based, and other modality companion diagnostics are not covered by the proposal. The comment period closed in January 2026. A final rule is anticipated but had not been published at the time of writing.

Programme Planning Implication

As Callum explains, the proposed reclassification is influencing planning conversations but very few sponsors are restructuring CDx regulatory roadmaps around it. The PMA route remains the most reliable assumption. If the reclassification is approved and the 510(k) route becomes available during development, the higher analytical and clinical rigour invested in a PMA programme can only offer an advantage when transitioning to a 510(k) pathway. The reverse, planning for 510(k) and then receiving FDA feedback requiring PMA, creates significant remediation cost.

Co-Development Timeline: What a Realistic Parallel Drug and CDx Programme Looks Like

For sponsors developing a drug and a companion diagnostic simultaneously, a realistic integrated programme is typically four to six years from biomarker confirmation to regulatory approval of both products. Aggressive programmes with mature biomarker readiness may compress to around three and a half years.

Development Phase	Typical Timeframe	CDx Programme Activity
Biomarker discovery and confirmation	Months 0–12	Define intended use concept; select assay technology; initiate pre-analytical controls
Prototype assay and fit-for-purpose validation	Months 12–24	Develop and validate CTA; initiate first FDA Pre-Submission
Clinical trial assay deployment	Months 18–36	IDE determination; IRB submission; analytical validation to GLP standards
Commercial assay lock and analytical validation	Months 24–42	Assay lock-down; design controls; assay bridging if needed; first PMA modules
Pivotal clinical performance study	Months 36–54	Clinical validation in the therapeutic trial; specimen banking; cross-referencing agreements
Regulatory submission, review, and approval	Months 48–72	Complete PMA submission; CDRH review; labelling alignment; contemporaneous approval target

The Critical Inflection Points Where CDx Programmes Fall Behind

Three structural failure modes recur across co-development programmes:

•  The drug programme evolves and the assay must evolve with it. Every major assay change after pivotal evidence generation has begun creates the potential for a bridging study, increasing the development burden and extending the timeline.Assay lock too late.
•  When the biomarker prevalence is low, common in rare disease and gene therapy indications, the pool of positive specimens available for analytical, bridging, and clinical studies is constrained. This limits statistical power and forces difficult decisions about study endpoints.Access to quality clinical samples.

 Low enrolment due to unexpectedly low biomarker positivity rates collapses the statistical power of the pivotal trial, making it impossible to calculate meaningful sensitivity and specificity estimates within the planned timeline.Misestimation of biomarker prevalence.

The most common and expensive mistake is treating the IVDR performance study as the diagnostic manufacturer’s problem rather than a shared sponsor responsibility. The pharmaceutical team and the diagnostics team operate on disconnected timelines, and the CDx submission is not integrated into the master trial timeline from the outset. For US programmes, the equivalent failure is submitting the IND months before the PSA or IDE application is even drafted. The structural fix is identical in both jurisdictions: from Day 1 of trial design, the diagnostic regulatory workstream sits inside the integrated trial timeline, with a named owner, shared document management, and joint governance between pharmaceutical and diagnostic functions.

Callum Pickett, Clinical Alliance Lead, MDx CRO

Pharma-IVD Partnership Governance: What the Contractual Framework Must Address

When the drug sponsor and the diagnostic manufacturer are separate legal entities, the most common configuration in oncology CDx, the partnership must resolve several foundational questions before clinical trials begin. The governance gaps that create the most regulatory risk are the following:

Data Sharing and Letters of Authorization

The diagnostic sponsor needs access to clinical outcome data from the drug trial to support clinical validation. The drug sponsor needs the diagnostic sponsor’s performance data to complete the NDA or BLA. Neither can finalise its FDA submission without the other. Data sharing rights and the flow of clinical specimens between institutions require contractual agreements that anticipate FDA’s requirement for Letters of Authorisation, these letters allow each sponsor’s submission to cross-reference the other’s proprietary data without transferring confidential information directly.

Timing Alignment and Contemporaneous Approval

FDA’s preferred model is contemporaneous approval, the CDx PMA and the drug NDA or BLA approved on the same day. Achieving this requires joint regulatory strategy sessions from the pre-IND stage, coordinated Pre-Submission meetings with CDRH and the drug review centre, and contract provisions that prevent either party from advancing or withdrawing an FDA submission unilaterally.

The Bridging Study Decision

The choice of which assay to use in the clinical trial determines whether a bridging study will be required after the pivotal study closes. This is one of the most consequential and most frequently misunderstood decisions in CDx programme management.

Trial Assay Used	Bridging Study Required?	Timing Risk
Final CDx device (commercial version)	No: direct clinical validation	Lowest
Early-version CDx or LDT with central confirmatory lab	Possibly	Moderate
LDT only, no central confirmation	Yes	High: can delay PMA 12 to 24 months

Bridging studies must demonstrate that patients selected by the clinical trial assay show equivalent clinical outcomes when retested on the final CDx. Both biomarker-positive and biomarker-negative samples from all screened subjects must be banked with confirmed analyte stability, and patient consent for retesting must be obtained at enrolment. Retroactive consent collection is nearly impossible in practice.

Bridging strategy is particularly scrutinised by CDRH. As Callum explains, sponsors often underestimate the evidentiary burden required to demonstrate that assay modifications do not compromise clinical validity. Late recognition of the need for bridging often creates avoidable regulatory risk. It is therefore important to consider bridging scenarios prospectively, even where the expectation is that the assay will remain stable.

Class and Group Labelling: When a Single CDx Can Cover a Therapeutic Class

FDA’s 2020 guidance on class and group labelling opened the door to a single CDx covering a therapeutic class rather than a named drug. The appeal is clear: it reduces the need for repeated companion diagnostic label updates each time an additional therapy within the same class is approved. In practice, however, this strategy is viable in a narrower set of circumstances than sponsors initially anticipate.

Successful class labelling requires a high degree of mechanistic uniformity across the therapeutic class: the biomarker must predict response across all relevant agents through the same underlying biological mechanism, clinical effect must be consistent with no material variation in the biomarker-response relationship between therapies, and the clinical evidence package must be capable of supporting a common claim across products. FDA’s approach remains cautious, and appropriately so, because overly broad class labelling carries the risk of inappropriate treatment selection if mechanistic or clinical differences between therapies are not adequately characterised.

Class labelling is most successful in highly mechanistically homogeneous targeted therapy classes with analytically stable biomarkers and consistent treatment paradigms. It is far less effective in settings characterised by heterogeneous response biology, variable lines of therapy, or differing combination regimens.

Breakthrough Devices Designation: When to Pursue It for a CDx

The Breakthrough Devices Programme is an optional FDA designation intended to facilitate development and expedite review of medical devices meeting defined statutory criteria. It is important to note that the Breakthrough designation is not a separate premarket pathway, it operates within the existing PMA, 510(k), or De Novo framework and provides enhanced engagement rather than a reduced evidentiary standard.

Under section 515B of the FD&C Act, a device may be designated as a Breakthrough Device if it provides more effective treatment or diagnosis of a life-threatening or irreversibly debilitating disease or condition and meets at least one of the following: it represents a breakthrough technology, no approved or cleared alternatives exist, it offers significant advantages over existing alternatives, or availability is in the best interest of patients.

In the CDx context, Breakthrough designation is most relevant where the assay is linked to a novel therapeutic addressing a serious condition with limited treatment options, or where the diagnostic enables access to a targeted therapy in a population with previously unavailable options. However, designation should not be pursued as a default strategy. It should be considered only where the statutory criteria can be robustly justified and where the programme is expected to derive tangible benefit from more interactive FDA engagement during development.

Assay Technology Selection: IHC, NGS, PCR, and ELISA in a CDx Context

Assay technology selection for a companion diagnostic is not a pure technical decision, it is a regulatory and commercial one. The technology determines the scope of analytical validation, the plausibility of a 510(k) pathway (where applicable), the level of software and algorithm documentation required by CDRH, and the ease with which the assay can be standardised across clinical sites.

Expert imput

When selecting a technology for the CDx assay, it is first important to consider the science. If the biomarker of interest is DNA- or RNA-based, NGS or PCR may be appropriate. If the biomarker is protein-based, IHC or ELISA should be considered. The current state-of-the-art for the detection of the analyte should be carefully reviewed to ensure the technology chosen reflects standard clinical practice. Analytically, the technology must be sufficiently sensitive and specific around the diagnostic cut-off, particularly for CDx devices, where the analytical performance around the cut-off directly influences patient management decisions.

FDA CDx in Rare Disease and Gene Therapy: Why These Programmes Are Harder

Rare disease and gene therapy CDx programmes present a specific set of structural challenges that generic CDx regulatory guidance does not adequately address. The challenges are not primarily regulatory, they are epidemiological.

The most common difficulty is sample availability. During analytical development, the limited patient population means that specimens positive for the biomarker of interest may be genuinely scarce. This constrains the options for bridging studies when the intended use needs to be extended to new sample types, and limits the ability to generate analytically sufficient datasets within normal development timelines.

In the clinical performance study, low enrolment numbers (a direct consequence of low disease prevalence) frequently mean there are too few samples to calculate diagnostic sensitivity and specificity with adequate statistical power. In these programmes, the objective and endpoints of the CDx performance evaluation must be carefully reconsidered. Rather than conventional accuracy metrics, the primary evidence may need to focus on clinical utility endpoints such as result turnaround time, quality control failure rate, or other parameters relevant to the specific clinical decision the device supports.

FDA and IVDR in Parallel: Structuring a Dual-Jurisdiction CDx Programme

When a sponsor wants to achieve both FDA approval and CE-IVDR marking for their CDx, the most important planning decision is identifying which parts of the development programme can be shared across the two frameworks, and which cannot. Making this determination at inception, not mid-programme, is what determines whether the parallel strategy is commercially viable within the intended timeline.

The intended use statement is the first element that can be aligned across jurisdictions. Both FDA and the IVDR require a clear, consistent intended use, and aligning this statement ensures that the development programme is synchronised so that data can be leveraged across both regulatory frameworks.

Analytical validation data can typically be leveraged across both, particularly if generated in accordance with CAP, CLIA, and CLSI guidelines. Both the IVDR and FDA’s 21 CFR Part 820 framework require comparable analytical parameters, sensitivity, specificity, accuracy, precision, interfering substances, and stability, before the device can be used in a clinical context.

The clinical performance study location introduces a jurisdiction-specific consideration. A study performed exclusively in the US or the EU may require justification of sample population equivalence for the other jurisdiction. Early dialogue with FDA through a Q-Submission, or with a Notified Body through pre-submission engagement, is the most efficient mechanism to establish whether the data from one population can support marketing in the other.

What a VP of Regulatory Affairs Should Ask When Evaluating a CDx Partner

Evaluating a CDx development partner requires questions that go beyond credentials and prior submission history.

The questions that most reliably separate capable partners from those that simply present well are the following:

• Does the team assigned to the CDx project understand the science behind the device and the clinical setting, not just the regulatory requirements?
• Does the partner have a regulatory intelligence system for continuous improvement and incorporating feedback from FDA to increase submission success rates?
• Does the partner have tried-and-tested templates and procedures that can be deployed quickly?
• What is the partner’s average number of RFIs received per submission and average time to resolution? If workload increases, can the partner scale the team with CDx-experienced personnel?

The RFI question is particularly diagnostic. The volume and complexity of requests for information during an FDA review directly reflects the quality of the initial submission. A partner that receives few RFIs or resolves them rapidly is demonstrating that its pre-submission preparation is calibrated to CDRH expectations, not merely producing technically complete documentation.

Summary: Key Decision Points in an FDA CDx Programme

Decision Point	Timing	Key Risk If Delayed
Intended use finalisation	Pre-IND / pre-trial design	All downstream validation, clinical, and labelling strategy misaligned
Significant risk determination	Before first clinical trial use	IDE applicability missed; study cannot proceed; IRB approval at risk
First Pre-Submission to CDRH	Once platform, specimen strategy, and analytical concept defined	Regulatory pathway misidentified; avoidable rework at submission
Assay lock	Before pivotal study enrolment	Bridging study required; 12–24 month delay; additional user fees
Letters of Authorisation between diagnostic and drug sponsors	Before pivotal study enrolment	Neither submission can be finalised; contemporaneous approval at risk
Pharmaceutical sponsor-CDx partner joint governance	Day 1 of programme	Disconnected timelines; IVDR/IDE workstream not integrated; delays at every stage

Frequently Asked Questions: FDA Companion Diagnostics

About MDx CRO: FDA Companion Diagnostic Development Services

MDx CRO is a specialist CRO in MedTech with core expertise in IVD regulatory strategy, IVDR clinical performance studies, and FDA companion diagnostic development. Our regulatory team has supported more than 40 combined drug-diagnostic programmes across Phase 1 to Phase 3 trials, across the EU, US, and Asia-Pacific.

Our FDA CDx services cover: companion diagnostic regulatory strategy (PMA, De Novo, 510(k)); Q-Submission and Pre-Submission preparation; significant risk determination and IDE support; analytical and clinical validation planning; assay bridging strategy; co-development governance frameworks; and EU-US parallel submission strategy.

Download our FDA Companion Diagnostic Roadmap Template, a structured planning document covering the full regulatory pathway from intended use definition to post-market obligations. Available to download from this page.