510(k) Submissions: Substantial Equivalence, eSTAR and What FDA Expects

Introduction

The 510(k) is the most common route to the US market for medical devices. Named after Section 510(k) of the Federal Food, Drug, and Cosmetic Act, it asks the manufacturer to demonstrate that a device is substantially equivalent to one already legally marketed, rather than to prove safety and effectiveness from first principles as a Premarket Approval requires.

That distinction is what makes the pathway fast, and it is also what makes it fail. A 510(k) is not an evidence exercise, it is a comparison exercise: almost every avoidable delay traces back to a predicate chosen badly, a difference from the predicate left unjustified, or an eSTAR section completed without the evidence behind it. The technology is rarely the problem.

This guide covers the four submission types and when each applies, how substantial equivalence is actually determined, when clinical data become unavoidable, what the FDA does and does not review, how the eSTAR template is structured, exemptions, fees, and what happens when equivalence cannot be demonstrated.

Table of Contents

• The four types of 510(k) submission
• Substantial equivalence: what is actually compared
• When clinical data become necessary
• Does the FDA review your QMS during a 510(k)?
• The eSTAR template in practice
• Exemptions, and their limits
• What happens after a Not Substantially Equivalent determination
• User fees and the Small Business Determination
• FDA-recognised consensus standards
• Where 510(k) submissions lose time
• Frequently asked questions
• Conclusions

The four types of 510(k) submission

The FDA recognises four routes. Choosing the wrong one costs a review cycle, and the choice is determined by what you are submitting rather than by how quickly you would like it reviewed.

The Special 510(k) is the one most often attempted and refused. The test is not whether the change is small in engineering terms — it is whether the change touches the intended use or the fundamental technology. A material substitution that leaves both untouched can be Special; a software change that adds a new claimed function cannot, however minor the code change was.

Substantial equivalence: what is actually compared

Substantial equivalence is the foundation of the pathway and the most misread concept in it. It does not mean identical. It means the device is as safe and as effective as a legally marketed predicate, judged on two axes: intended use, and technological characteristics.

The comparison runs across intended use, indications for use, design features, materials, energy source and performance characteristics. Innovation is permitted — the pathway assumes devices improve — provided the improvements do not raise different questions of safety and effectiveness.

The decision has a defined shape, and understanding it is what makes a comparison table persuasive rather than descriptive.

Two consequences follow from the shape of that path. The first is that a difference in technological characteristics is not fatal — it moves the burden to performance data. The second is that a difference in intended use is fatal, and no amount of testing repairs it. This is why predicate selection is a regulatory decision taken at the start of a project rather than a documentation task at the end.

When clinical data become necessary

Most 510(k) submissions do not include clinical data, meaning data from investigations conducted on human subjects. The assessment of whether they are needed belongs at the start of the project, before the submission is drafted, because generating them later resets the timeline entirely.

Four circumstances make them necessary:

• The predicate’s own clearance was supported by clinical data.
• Differences between the subject device and the predicate cannot be adequately justified without them.
• Substantial equivalence cannot be demonstrated by any other means.
• The FDA requests them explicitly.

Software as a Medical Device sits in a particular position. Clinical data in the classical sense are usually not required, because the device collects, processes or analyses information rather than delivering a therapeutic intervention. What the FDA does require is adequate performance evaluation, and for an algorithm that generally means testing against real clinical data — either through a formal clinical investigation, or by obtaining existing clinical datasets and demonstrating performance against them without a new study. The classification questions that determine which applies are covered in our guide to Software as a Medical Device classification and regulatory pathway.

Does the FDA review your QMS during a 510(k)?

No, and the answer is more consequential than it sounds. The 510(k) review examines the technical documentation of the device. The quality management system is not assessed as part of it.

That is not permission to defer the quality system. Marketing a device in the United States requires compliance with the Quality Management System Regulation, which since February 2026 incorporates ISO 13485 by reference into 21 CFR Part 820. The obligation applies from the moment the device is marketed, and it is enforced through inspection rather than through the clearance decision.

The practical trap is sequencing. A manufacturer that treats clearance as the finish line arrives at its first FDA inspection with a device on the market and a quality system that was never built. The two workstreams run in parallel, and only one of them has a visible deadline.

The eSTAR template in practice

510(k) submissions are prepared in eSTAR — the electronic Submission Template And Resource — an interactive PDF that guides the applicant through a structured series of questions and attachment points. It is downloaded from the FDA website and it is adaptive: sections appear or disappear according to the device’s classification, intended use and technological characteristics, so no two submissions have quite the same shape.

For a single-use, non-active device the sections typically present are these.

The biocompatibility section deserves separate attention because it is where incomplete submissions are most often caught. The evaluation is built per the FDA-modified ISO 10993-1 matrix, contact type by contact duration, and chemical characterisation is expected rather than optional for most material families. Our guide to biocompatibility testing under ISO 10993 sets out the matrix and what the FDA expects against each cell of it.

eSTAR performs a completeness check before the FDA does. That check confirms that attachments exist, not that they say anything. A submission can pass the technical screening with a performance report that tests the wrong thing, and the first sign of trouble will be an Additional Information request sixty days later.

Exemptions, and their limits

Many Class I devices and a limited number of Class II devices are exempt from 510(k) notification, on the basis that they are low risk and raise no significant questions of safety or effectiveness. The FDA maintains the list by product code.

Exemption from notification is not exemption from regulation. An exempt device is still subject to establishment registration and device listing, labelling requirements, and the quality management system requirements. The manufacturer still holds the obligations; it simply does not file a premarket notification.

Two limits are easy to trip over. Exemptions are subject to limitations set out in the regulation for each device type — typically expressed as a ceiling on what the device may claim or how it may be constructed — and a device that exceeds them loses the exemption. And a device with novel features, a new intended use, or a significant deviation from the exempt device type falls outside the exemption regardless of its classification.

What happens after a Not Substantially Equivalent determination

When equivalence cannot be demonstrated, the FDA issues a Not Substantially Equivalent determination. The device cannot be marketed through the 510(k) route, and the manufacturer has two alternatives.

The De Novo route is frequently the right answer for a genuinely novel low-risk device, and it is worth understanding before an NSE forces the question — the requirements, the special controls and the submission structure are covered in our guide to the FDA De Novo pathway. An NSE determination reached after a failed 510(k) costs a full review cycle that a De Novo filed first would not have.

User fees and the Small Business Determination

A user fee is payable with every 510(k) unless the submitter qualifies for the reduced small business rate. The standard and small business fees are set annually by the FDA and change each fiscal year, so the figure has to be checked against the current fee schedule rather than carried over from a previous submission.

The reduced rate requires a Small Business Determination, obtained by submitting FDA Form 3602 — or Form 3602A for a foreign business — through the FDA portal. The determination is issued as a Small Business Decision number, valid for the fiscal year, and it must be renewed annually.

The SBD number has to be in hand before the 510(k) is submitted. A submission filed without it is charged the full fee, and the fee cannot be refunded or adjusted retrospectively. Since the determination takes weeks and the number expires each fiscal year, this belongs on the project timeline rather than on the submission checklist.

FDA-recognised consensus standards

The FDA maintains a list of recognised consensus standards developed by bodies such as ISO, IEC and ASTM, covering testing methods, performance evaluation, biocompatibility, electrical safety and software. Conformity to a recognised standard serves as objective evidence against the requirement it covers, and for well-characterised device types it can remove the need for additional testing entirely. This is the mechanism the Abbreviated 510(k) is built on.

Claiming conformity carries an obligation. The submission must include a declaration of conformity and the test reports or evidence supporting it — a standard cited without evidence is a claim, not a demonstration. The eSTAR template has a dedicated section for recording which standards have been applied.

One detail is worth checking each time: the FDA recognises specific editions of standards, and the recognition can lag the current published edition. Testing performed to the newest edition of a standard the FDA has not yet recognised at that edition is not automatically accepted, and the transition periods are published alongside the recognition list.

Where 510(k) submissions lose time

A predicate chosen for convenience. The nearest cleared device is not necessarily the right predicate. The one that matches on intended use matters more than the one that matches on technology, because a difference in technology moves the burden to data while a difference in intended use ends the pathway.

Differences described rather than justified. A comparison table that lists what differs, without explaining why the difference raises no new question of safety or effectiveness, has done half the work. The justification is the submission.

A Special 510(k) filed for a change that is not eligible. The submission is converted to Traditional and the clock restarts, having spent the review time establishing that the route was wrong.

Biocompatibility built on the standard rather than on the FDA modification. The FDA-modified matrix differs from ISO 10993-1 as published, and a biological evaluation constructed from the ISO version alone will have gaps against the FDA’s expectations.

Performance testing with acceptance criteria set after the results. Criteria derived from the data they are meant to judge are visible as such, and they invite the question of what would have counted as failure.

The quality system deferred until after clearance. Clearance permits marketing; marketing triggers the QMSR obligations immediately. The inspection does not wait for the system to be ready.

Frequently asked questions

What is a 510(k) submission?

A 510(k) is a premarket notification to the FDA demonstrating that a device is substantially equivalent to a legally marketed predicate device. It is required for most Class II devices and for some Class I devices before they may be marketed in the United States, and it is named after Section 510(k) of the Federal Food, Drug, and Cosmetic Act.

What are the types of 510(k) submission?

Four: Traditional, which is the default and always available; Abbreviated, which relies on FDA-recognised consensus standards, guidance documents or special controls in place of repeating testing; Special, for modifications to a device the manufacturer has already had cleared, where the change affects neither the intended use nor the fundamental scientific technology; and Third Party, for eligible device types reviewed by an FDA-accredited organisation.

What is substantial equivalence?

Substantial equivalence means the device is as safe and as effective as a legally marketed predicate. It does not mean identical. The determination compares intended use and technological characteristics: a different intended use ends the pathway, while different technological characteristics are acceptable if performance data show they raise no different questions of safety and effectiveness.

Do I need clinical data for a 510(k)?

Usually not. Clinical data become necessary when the predicate’s clearance was itself supported by clinical data, when differences from the predicate cannot be justified without them, when equivalence cannot be demonstrated by any other means, or when the FDA requests them. For Software as a Medical Device, formal clinical investigations are often unnecessary, but performance evaluation against real clinical data is expected.

Does the FDA review my quality management system during a 510(k)?

No. The 510(k) review examines the technical documentation of the device. Compliance with the Quality Management System Regulation, which incorporates ISO 13485 by reference, is nonetheless mandatory for marketing a device in the United States and is enforced through inspection rather than through the clearance decision.

What is eSTAR?

eSTAR is the interactive PDF template used to prepare 510(k) submissions. It is downloaded from the FDA website and adapts to the device: sections appear or are omitted according to classification, intended use and technological characteristics. It performs a completeness check before submission, confirming that attachments are present — not that their content is adequate.

What happens if my device is found Not Substantially Equivalent?

The device cannot be marketed through the 510(k) pathway. Two alternatives remain: the De Novo classification request, appropriate for a low to moderate risk device with no suitable predicate, which results in classification into Class I or II; or Premarket Approval, for higher-risk devices, which requires far more extensive evidence and usually clinical data.

How do I get the reduced 510(k) fee?

By obtaining a Small Business Determination from the FDA before submitting, using Form 3602 for a domestic business or Form 3602A for a foreign one. The resulting Small Business Decision number must be included in the submission, is valid for the fiscal year, and must be renewed annually. A submission filed without it is charged the full fee, with no retrospective adjustment.

Conclusions

The 510(k) is an efficient pathway because it substitutes comparison for proof. That efficiency is conditional: it holds only as long as the comparison is sound, and it collapses the moment the predicate turns out to be the wrong one.

Three decisions carry most of the risk, and all three are taken early. The predicate, because intended use cannot be repaired with data. The submission type, because a Special 510(k) refused converts to a Traditional with the review clock reset. And the parallel build of the quality system, because clearance permits marketing and marketing triggers QMSR obligations that the clearance decision never examined.

If you are building the quality system alongside the submission, the ISO 13485 Documentation Kit covers the full QMS scope aligned with the FDA QMSR, and the MDSAP Documentation Kit extends it to the four other MDSAP markets if the United States is not the only destination.

Related articles

• FDA De Novo Pathway: When to Use It and How to Submit
• Biocompatibility Testing for Medical Devices: ISO 10993 Complete Guide
• Software as a Medical Device (SaMD): Classification and Regulatory Pathway
• ISO 13485:2016 — The Complete Guide to Medical Device Quality Management
• MDSAP Audits
• ISO 14971 Risk Management for Medical Devices