The label says RUO. FDA reads intent.

Research Use Only and Investigational Use Only are the two phrases on an in vitro diagnostic’s label that let it skip the review a clinical claim would otherwise require. Put one of them on the box, honestly, and the product can ship without a 510(k), a De Novo, or a PMA. FDA has spent more than a decade making a different point in writing: the sentence on the label is not the fact that controls. What the manufacturer is actually doing with the product is.

What the label is allowed to replace

21 CFR 809.10(c)(2) writes the exemption’s terms exactly: a product “in the laboratory research phase of development” that is not represented as an effective diagnostic may carry, in place of ordinary IVD labeling, one of two sentences the regulation itself supplies — “For Research Use Only. Not for use in diagnostic procedures,” or “For Investigational Use Only. The performance characteristics of this product have not been established.” Either sentence, placed prominently, is a self-executing claim. Nobody at FDA signs off on it before the product reaches a lab.

A 2013 guidance named what the label doesn’t settle

FDA finalized Distribution of In Vitro Diagnostic Products Labeled for Research Use Only or Investigational Use Only on November 25, 2013, after a 2011 draft had proposed something sharper: a manufacturer who merely had “reason to know” a customer was running its RUO product diagnostically would have to cut the customer off. FDA dropped that standard from the final guidance. What replaced it was narrower, and arguably more durable — FDA judges a manufacturer’s objective intent, read from everything around the label rather than the label itself: marketing and advertising that make clinical claims, sales representatives soliciting business from diagnostic labs rather than researchers, technical support that reads like help validating a clinical assay, and distribution records naming customers who are, by any ordinary definition, clinical laboratories.

The label is the manufacturer’s claim about the product. The guidance is FDA’s answer that a claim is not evidence, and everything else the manufacturer does is.

The letters that followed are rare, and specific

FDA’s own warning-letter record on this theory is thin by design. Agena Bioscience, Inc. drew one in March 2024 over its iPLEX HS Colon Panel on the MassARRAY4 system, labeled RUO. FDA’s letter did not stop at the label. It cited distribution records and customer lists showing shipment to clinical testing laboratories, a customer notification about a rise in false-negative results, a user guide written to help interpret clinical reports, and website language describing the product in clinical, not research, terms — evidence FDA read as showing the panel was, despite its label, a new or significantly modified version of a factor-genotyping test the firm already held a 510(k) for.

What no record shows

There is no FDA database of which IVD products currently carry an RUO or IUO label. The status is self-applied by the manufacturer through labeling alone; nothing registers it, and nothing has to. A competitor’s RUO-labeled product, read from the outside, offers no public trail at all — not a filing, not a classification entry, nothing in the clearance record this product watches. The same silence covers a CLIA-certified lab building its own laboratory-developed test on an RUO component: CLIA’s quality rules in 42 CFR Part 493 govern how the lab runs the test, not which IVD inputs it is allowed to use, and nothing in that record says whether FDA would read the input’s distribution the way it read Agena’s.

The practice

Reading “RUO” or “IUO” on a label as the end of the inquiry treats a self-applied claim as if it were a clearance. FDA’s own guidance and its own enforcement history both say otherwise: the label is where the question starts, and the manufacturer’s marketing, sales, and support conduct is where FDA actually looks. RUO and IUO status sits outside the four sources this product ingests — Federal Register notices, warning letters, device recalls, and 510(k) clearances, listed on what we monitor and what we deliberately don’t — except at the rare moment enforcement catches up to a specific product, the way it did with Agena’s, and surfaces in a warning letter this product does read. Whether a specific RUO or IUO claim reflects the product’s actual intended use is a determination for the firm making it and, eventually, FDA — this is a description of the standard FDA applies, never a review of any product’s labeling.