The letter to file isn't in the guidance

Every device-quality team that has ever decided a design change didn’t need a new 510(k) calls the record of that decision a “letter to file.” Search FDA’s own guidance on the subject for that phrase and it isn’t there. The agency has a name for what that record is supposed to contain. It isn’t a letter, and the guidance never calls it one.

What the guidance actually asks

Deciding When to Submit a 510(k) for a Change to an Existing Device is FDA’s current guidance on the question, finalized October 25, 2017 and replacing a 1997 version of the same title. It is built around a single decision flowchart, then a set of lettered flowcharts underneath it for specific kinds of change — labeling, technology or engineering or performance, and materials — plus a dedicated section for in vitro diagnostics. Every path through every one of those flowcharts ends at one of exactly two places: submit a new 510(k), or document the basis for not submitting one. That second phrase — document the basis for the decision — is the guidance’s own language. “Letter to file” is not in it.

The test underneath the flowchart

The flowcharts exist to apply one regulation, 21 CFR 807.81(a)(3): a cleared device needs a new premarket notification when it is changed or modified enough to significantly affect safety or effectiveness, or when its intended use changes in a major way. The guidance’s whole contribution is translating that test into a risk-based comparison against the device as it was most recently cleared — not as it was originally designed, and not as a competitor’s similar device was cleared. What changed, and whether the change could move the device’s risk profile relative to that specific, most recent clearance, is the question every flowchart branch is really asking.

A flowchart with two endpoints doesn’t have a third. “Flag it for next quarter” or “note it and move on” are not outcomes the guidance recognizes — a team that reaches for either one has stopped following FDA’s own decision tree partway through.

Where the industry’s name for it actually comes from

“Letter to file” predates this guidance by years and has nothing to do with it — it is quality-system shorthand for a documented record kept inside a device’s own design and development records, the kind every manufacturer has to maintain independent of any single 510(k) decision. The 2017 guidance didn’t invent the practice of documenting a no-new-510(k) decision; manufacturers were already required to keep that reasoning somewhere defensible. What the guidance did was give the decision itself a structure — the flowcharts — without ever adopting the name the industry had already settled on for where the answer gets written down.

The practice

The distinction is not pedantic. A reviewer or an investigator who goes looking for “the letter to file” is asking an informal question; what they actually need to find is the flowchart followed, the specific most-recent clearance compared against, and a documented, risk-based reason the change doesn’t clear the 807.81(a)(3) bar — in whatever form a firm’s own quality system keeps that reasoning. A one-line note that says “no new 510(k) needed” satisfies the industry’s name for the document and fails the guidance’s actual test, because it skips the comparison the flowchart exists to force.

FDA Radar’s 510(k) feed keeps a device’s own clearance history — K-number, product code, decision date — visible as exactly the baseline this comparison runs against; see what we monitor and how often. Whether a specific change clears that bar is a determination for the regulatory professional reading the specific device file, never a determination this product makes for you — this is regulatory intelligence and method, never regulatory advice.