The Applied Science Blog

 Bringing a medical device to market isn’t just about great engineering—it’s about making sure real people can use it safely and effectively. Many companies underestimate this until it’s too late. Human factors and usability issues are one of the top reasons FDA 510(k) submissions get delayed or rejected, forcing teams into costly redesigns, repeat testing, and months of lost market time.

From infusion pump overdoses caused by overly complex programming to diagnostic devices recalled for confusing interfaces, history shows that poor usability isn’t just an inconvenience—it can harm patients and derail product launches. In fact, FDA data shows that a significant share of first-round submissions receive additional information requests, often due to usability-related deficiencies.

Most of the insights in this article draw from the FDA’s official guidance document Applying Human Factors and Usability Engineering to Medical Devices and industry analysis like this FDA Law Blog post. A special thanks to the FDA team for making these resources available and for providing ongoing feedback that helps manufacturers understand and meet usability expectations.

In the following section, we translate those lessons into practical, real-world recommendations backed by actual case studies. These are the usability practices that can help you avoid costly delays, build safer devices, and navigate FDA clearance with confidence.

 Recommendation: Begin formative (exploratory) usability testing early in development and follow with a robust summative (validation) test.

Why it matters: Without early iteration, final validation often uncovers critical flaws that require redesign and repeat testing—leading to costly FDA additional information (AI) requests and delays. Approximately 30% of 510(k)s fail initial review, and human factors deficiencies are a leading cause.

Example: A firm rushed a summative usability test due to schedule pressure, only to have FDA reject it for insufficient task risk analysis—forcing a full re‑test and delaying submission by 6+ months, costing tens of thousands in additional work.

Recommendation: Define all intended user types separately (e.g. nurses, physicians, home users) and conduct usability validation with each group, covering all critical safety tasks.

Why: The FDA typically expects 15 participants per distinct user group, and combining groups without justification invites review questions and delays source.

Example: A patient monitor developer grouped nurses and cardiologists together in usability testing. FDA flagged this grouping and requested additional data, delaying the submission while additional group-specific testing was conducted.

Recommendation: Address use-risk through design changes first. Training or labeling should be secondary, and validated so users follow instructions correctly.

Why: FDA doesn’t accept “we’ll fix in training” unless backed by evidence. Real-world usability safety comes from intuitive design, not instruction manuals.

Example: A PCA infusion pump caused serious overdoses via a multi-step programming interface. The manufacturer initially relied on training, but FDA required redesign. After redesign, programming steps were simplified by 55% and errors dropped 56%, ending the safety issue source.

Recommendation: Conduct validation tests under conditions mimicking actual settings: noise, lighting, PPE usage, time pressure, fatigue, etc.

Why: Tests that fail to reflect clinical realities may be rejected, forcing repeat testing. FDA requires “sufficiently realistic” environments tied to risk context source.

Example: A pulse oximeter was tested in ideal light but failed under low-light nighttime conditions, a problem only discovered post-launch and reported as user usability failures—leading to complaint and corrective action.

Recommendation: During summative testing, do not coach participants. Report all critical task outcomes, and pre-define data exclusion criteria, replacing participants if needed.

Why: Coaching or excluding “bad” data damages integrity. FDA reviewers will question manipulated results, triggering additional information requests or test repetition source.

Example: One company trimmed validation data by excluding a participant who made a critical error—without justification. FDA raised the issue, demanded full raw data review, and the submission stalled while the study was redone with a full, transparent dataset.

Recommendation: Create a detailed Use‑Related Risk Analysis (URRA) and document observed usability issues with root‑cause analyses and mitigations. Maintain a Usability Engineering File per IEC 62366‑1/ISO 14971.

Why: FDA deficiencies often cite poor URRA or superficial error documentation. A strong traceable analysis reduces questions and accelerates clearance source.

Example: A device submitted with a generic FMEA instead of task‑focused URRA was flagged, costing weeks to construct proper use-error analysis and delaying clearance. Another company’s submission included a clearly traceable table of error‑cause‑mitigations, impressing FDA and speeding review.

• Up to 30% of 510(k)s fail the first review, and human factors is a critical failure point in many cases source.
   
• FDA has stated that even a single critical task triggers human factors requirements—even if the predicate didn’t require it source.
   
• Companies integrating usability engineering early and documenting comprehensively can often clear FDA in one cycle—a rare success, but achievable with rigor.

• Success Case: A home-use therapeutic device underwent early formative testing, had separate summative studies for patients and clinicians, incorporated realistic home environment simulations, and provided a clean URRA with corrective design iterations. FDA cleared it with no human factors questions—enabling on-schedule market entry.
   
• Failure Case: A Class II device used expedited UI development and deferred usability until late. The validation test had one user group, was conducted in quiet lab conditions, and sunscreened over a user error. FDA sent a human factors deficiency letter citing all these issues—delaying clearance by 4–6 months while new studies and analyses were conducted.