Why your literature review keeps failing Notified Body scrutiny
I see the same pattern in every third CER submission: the literature review section looks complete, contains dozens of references, demonstrates effort. Yet the Notified Body flags it for major deficiencies. The problem is rarely the quantity of literature. The problem is the method used to identify, select, and appraise that literature.
In This Article
Most manufacturers believe that conducting a thorough literature search and summarizing the findings is sufficient. They present comprehensive narratives about their device category, clinical context, and available evidence. They reference guidelines, textbooks, and published studies.
Then the assessment comes back: “The literature review does not demonstrate a systematic approach as required under MDR Article 61 and Annex XIV Part A.”
The core issue is methodological. The MDR framework, supported by MDCG 2020-13 and MDCG 2020-6, requires that clinical evaluation be based on a systematic and transparent process. When reviewers assess your literature component, they are not simply checking whether you found relevant papers. They are checking whether your method for finding those papers can be trusted, reproduced, and defended.
This distinction separates two fundamentally different approaches: the systematic review and the narrative review.
The Regulatory Expectation Under MDR
MDR Article 61(3) and Annex XIV Part A describe clinical evaluation as a systematic and planned process. The word “systematic” appears repeatedly throughout MDCG guidance documents for good reason.
A systematic approach means that every decision in the review process is predefined, documented, and executed according to explicit criteria. The search strategy is defined before searching begins. The inclusion and exclusion criteria are established before screening articles. The quality appraisal is conducted using validated tools before drawing conclusions from the data.
This structure protects the clinical evaluation from bias, selective reporting, and subjective interpretation. It creates an audit trail that allows any reviewer to understand exactly how you reached your conclusions.
When Notified Bodies and competent authorities assess your CER, they expect to see this systematic structure clearly documented. They expect to be able to follow your reasoning from search terms to final conclusions.
The MDR does not explicitly mandate a “systematic review” by name, but it mandates a systematic process. MDCG 2020-13 makes clear that clinical evaluation must follow rigorous, predefined, and transparent methods. In practice, this means adopting systematic review methodology.
What Is a Narrative Review?
A narrative review is a traditional literature summary. The author searches the literature, reads relevant papers, synthesizes the information, and presents an overview of the topic.
Narrative reviews are valuable in clinical practice and medical education. They provide context, expert interpretation, and accessible summaries of complex topics. Many published review articles are narrative in nature.
But narrative reviews have inherent limitations that make them unsuitable as the sole basis for regulatory decision-making:
No predefined search strategy. The author may search multiple databases, but the exact search terms, date ranges, and Boolean logic are rarely documented in reproducible detail.
Subjective article selection. The criteria for including or excluding studies are not always explicit. The author may select studies based on perceived relevance or quality without transparent rules.
Variable quality appraisal. Some narrative reviews critically appraise the evidence. Many do not. When they do, the appraisal criteria are often implicit rather than standardized.
Risk of selective reporting. Without predefined protocols, narrative reviews can inadvertently emphasize studies that support a particular viewpoint while underweighting contradictory evidence.
These limitations do not mean narrative reviews are worthless. They mean narrative reviews cannot serve as the primary evidence base for a clinical evaluation under MDR.
Manufacturers conduct a general literature search, summarize the findings in a well-written narrative, and assume this satisfies MDR requirements. The Notified Body then requests a complete redo with systematic methodology. Months of work become unusable because the foundational method was incorrect.
What Is a Systematic Review?
A systematic review is a structured research method designed to minimize bias and maximize transparency. It follows a predefined protocol that is established before the review begins.
The protocol defines:
Explicit research question. Usually formatted using PICO (Population, Intervention, Comparator, Outcome) or a similar framework. The question drives every subsequent decision.
Comprehensive search strategy. All databases, search terms, Boolean operators, date ranges, and language restrictions are documented. The strategy is designed to capture all relevant literature, not just convenient or familiar sources.
Predefined inclusion and exclusion criteria. Before screening begins, the protocol specifies exactly what types of studies will be included based on study design, population, intervention, outcome measures, and publication type.
Transparent screening process. Articles are screened in stages: title and abstract screening, then full-text screening. Each exclusion is documented with the reason. Ideally, two reviewers screen independently to reduce bias.
Standardized quality appraisal. Each included study is critically appraised using validated tools appropriate to the study design. For example, randomized controlled trials may be appraised using the Cochrane Risk of Bias tool, while observational studies may use the Newcastle-Ottawa Scale or similar instruments.
Structured data extraction. Relevant data from each study are extracted into standardized tables. This allows for transparent comparison and synthesis.
Documented synthesis. The findings are synthesized according to predefined methods. Depending on the data, this may be a narrative synthesis with thematic analysis, a quantitative meta-analysis, or both.
The result is a transparent, reproducible process that can withstand scrutiny from any reviewer.
Why This Matters for Your CER
When a Notified Body reviews your clinical evaluation report, they are assessing the reliability of your evidence base. They need confidence that your conclusions are supported by all relevant evidence, not just the evidence you happened to find or chose to include.
If your literature review is narrative, the reviewer cannot verify this. They cannot reproduce your search. They cannot confirm that you applied consistent criteria. They cannot assess whether important studies were missed or excluded without justification.
But here is the practical problem many manufacturers face: conducting a full systematic review requires significant time, expertise, and resources. It is not a one-week task. Depending on the scope, a properly conducted systematic review can take several months.
So what is the solution?
The solution is not to avoid systematic methods. The solution is to scope your review appropriately and apply systematic methods within that scope.
You do not need to review every piece of literature ever published on your clinical domain. You need to systematically review the literature relevant to your specific device, indication, and safety/performance claims. A focused systematic review with a well-defined research question is both achievable and defensible.
The Hybrid Approach in Practice
In real-world clinical evaluation work, we often use a structured combination of methods:
Background narrative review. A narrative overview establishes clinical context, disease epidemiology, current standard of care, and the unmet clinical need your device addresses. This section does not need to be systematic. It provides the reader with the necessary background to understand your device and its intended purpose.
Systematic literature review. The core evidence review is conducted systematically. This focuses specifically on literature relevant to your device type, technology, clinical application, and key safety and performance outcomes. The search strategy, inclusion criteria, quality appraisal, and synthesis are all documented according to systematic review methodology.
Targeted supplementary searches. For specific questions that arise during the evaluation, you may conduct additional focused searches. These should still be documented with clear search terms and criteria, but they may be more limited in scope.
This combination allows you to provide comprehensive clinical context while maintaining the rigor required for the evidence base that directly supports your safety and performance conclusions.
Common Mistakes I See Repeatedly
Mistake 1: Calling it systematic without the methodology. The CER states that a “systematic literature review” was conducted, but the appendix shows only a list of databases searched and a summary table of findings. No search strings, no PRISMA flow diagram, no documented screening process, no quality appraisal.
Mistake 2: Retrospective justification. The literature search is conducted first, and then inclusion criteria are written to match the studies that were found. This defeats the purpose of predefined criteria and introduces bias.
Mistake 3: Incomplete documentation. The systematic review was actually conducted properly, but the documentation is insufficient. Search strings are mentioned but not fully reproduced. Quality appraisal is referenced but the completed appraisal forms are not included. Reviewers cannot verify the work.
Mistake 4: Over-reliance on secondary sources. The review relies heavily on existing review articles, guidelines, and meta-analyses rather than identifying and appraising primary studies. Secondary sources are useful for context, but they cannot replace a direct assessment of primary evidence.
Mistake 5: Ignoring negative or inconclusive evidence. The review includes studies with positive outcomes but excludes or minimizes studies with complications, device failures, or inconclusive results. This selective reporting undermines the entire evaluation.
Manufacturers present a literature review with 50 references and assume this demonstrates thoroughness. The Notified Body asks: “How did you identify these 50 studies? What databases were searched? What were the search terms? How many studies were screened? Why were other studies excluded?” Without systematic methodology, these questions cannot be answered convincingly.
Practical Implications for Your Work
If you are preparing a new CER or updating an existing one, start with the research question. Define it clearly using a structured framework like PICO. This question will determine the scope of your systematic review.
Develop your search strategy before you begin searching. Document every database, every search term, every filter. Test the strategy to ensure it captures known relevant studies. Save the complete search strings so they can be reproduced.
Predefine your inclusion and exclusion criteria. Write them down. Have them reviewed by someone else to ensure they are clear and objective.
Screen systematically. Use a two-stage process: title and abstract first, then full text. Document every exclusion with the reason. If resources allow, use two independent reviewers.
Appraise quality using validated tools. Do not simply describe study design. Assess risk of bias, methodological quality, and relevance to your research question. Document the appraisal for each included study.
Synthesize transparently. If the data allow quantitative synthesis, consider meta-analysis. If not, conduct a structured narrative synthesis with clear thematic organization. Make it clear how individual study findings contribute to your overall conclusions.
Document everything. The appendices of your CER should contain the search strategy, the PRISMA flow diagram showing the screening process, the quality appraisal forms, and the data extraction tables. A reviewer should be able to follow your entire process from start to finish.
When Can Narrative Elements Be Used?
Narrative elements are appropriate and useful in several parts of the CER:
Device description and intended purpose. A clear narrative explanation of what the device is, how it works, and what it is intended to achieve.
Clinical background and context. A narrative overview of the disease or condition, current treatment options, clinical pathways, and the rationale for your device.
Interpretation and discussion. After presenting the systematic evidence, a narrative discussion that interprets the findings, explains their clinical significance, and addresses limitations.
State of the art. While the SOTA analysis should be evidence-based, it often includes narrative elements that describe the evolution of technology, emerging trends, and clinical practice patterns.
The key is that narrative elements support and contextualize the systematic evidence. They do not replace it.
What Notified Bodies Look For
When reviewing the literature component of your CER, Notified Bodies assess several specific elements:
Reproducibility. Can another person replicate your search using the documented strategy and obtain the same set of studies?
Transparency. Are all decisions documented and justified? Can the reviewer follow your reasoning at every step?
Completeness. Did the search strategy capture all relevant literature, or are there obvious gaps?
Objectivity. Are the inclusion criteria and quality appraisal applied consistently, or is there evidence of selective reporting?
Appropriateness. Is the review scope appropriate for the device and claims? Are the study designs and outcome measures relevant?
If any of these elements are weak, the literature review will be flagged. And because the literature review forms the foundation of the entire clinical evaluation, deficiencies here can cascade into deficiencies in every subsequent section.
A properly conducted systematic review is not just a regulatory requirement. It is a quality control mechanism that protects your entire clinical evaluation from bias and gaps in evidence. The extra effort invested in systematic methodology pays dividends in fewer deficiencies, faster approvals, and stronger post-market defensibility.
Final Thoughts
The distinction between systematic and narrative review is not academic. It is a practical dividing line between clinical evaluations that meet MDR requirements and those that do not.
A narrative review may be easier and faster to produce, but it will not satisfy Notified Body scrutiny. A systematic review requires more time and expertise, but it creates a defensible evidence base that supports your device throughout its lifecycle.
If your current CER relies on narrative literature review, the question is not whether you need to transition to systematic methods. The question is when and how you will make that transition.
Because every submission cycle that passes with narrative methods is another cycle that will likely result in major deficiencies and rework.
Start with the research question. Define your scope. Apply systematic methods within that scope. Document everything.
The regulatory pathway becomes clearer when the methodology is sound.
Peace,
Hatem
Clinical Evaluation Expert for Medical Devices
Follow me for more insights and practical advice.
Frequently Asked Questions
What is a Clinical Evaluation Report (CER)?
A CER is a mandatory document under MDR 2017/745 that demonstrates the safety and performance of a medical device through systematic analysis of clinical data. It must be updated throughout the device lifecycle based on PMCF findings.
How often should the CER be updated?
The CER should be updated whenever significant new clinical data becomes available, after PMCF activities, when there are changes to the device or intended purpose, and at minimum during annual reviews as part of post-market surveillance.
What causes CER rejection by Notified Bodies?
Common reasons include inadequate equivalence demonstration, insufficient clinical data for claims, poorly structured SOTA analysis, missing gap analysis, and lack of clear benefit-risk determination. Structure and logical flow are as important as the data itself.
Which MDCG guidance documents are most relevant for clinical evaluation?
Key documents include MDCG 2020-5 (Equivalence), MDCG 2020-6 (Sufficient Clinical Evidence), MDCG 2020-13 (CEAR Template), MDCG 2020-7 (PMCF Plan), and MDCG 2020-8 (PMCF Evaluation Report).
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Peace, Hatem
Your Clinical Evaluation Partner
Follow me for more insights and practical advice.
– Regulation (EU) 2017/745 (MDR), Article 61 and Annex XIV Part A
– MDCG 2020-13: Clinical evaluation assessment report template
– MDCG 2020-6: Regulation (EU) 2017/745: Sufficient clinical evidence for legacy devices
