FDA Abandons Its Defense of the LDT Rule, But is It Signaling an Increase in RUO Scrutiny?

At midnight on Friday, May 30, 2025, the government’s deadline to notice an appeal from the U.S. District Court for the Eastern District of Texas’s decision vacating the LDT Rule lapsed without the government doing so. This means the District Court decision stands, with no further right of appeal, and the LDT Rule remains vacated in its entirety.  As HPM argued in both the groundbreaking citizen petition Jeffrey Gibbs filed thirty-two years ago and the papers we filed on behalf of our clients, Dr. Michael Laposata and the Association for Molecular Pathology in the recent LDT litigation, the Federal, Food, Drug, and Cosmetic Act does not authorize FDA to regulate LDTs as medical devices. Those in the lab industry – and the physicians and patients who rely upon LDTs – are sure to be breathing a well-deserved sigh of relief over this development.

Just before this decisive event, though, FDA released a relatively rare Warning Letter to a manufacturer of research use only (RUO) reagents.  RUO-labeled reagents and materials are often used in LDTs in clinical laboratories.  The letter, which FDA issued on March 31, 2025 (but only posted on its website last week), was only one of two that FDA has sent in the last five years and only one of five that FDA has issued since finalizing its RUO Guidance in November 2013 (see guidance here).

The Warning Letter to DRG Instruments GmbH states that FDA determined the Company’s RUO‑labeled assay was intended for clinical diagnostic use, citing statements on the company’s website and labeling, as well as records that showed distribution to clinical laboratories that did not perform any research. Some of the claims that FDA cited as being for diagnostic use included “Simple and patient-friendly measurement of hormone profiles,” “Provides accurate, low level detection,” and “Can be performed also by patients.”

A striking detail in this Warning Letter was that FDA found it did not matter that the company had certification letters on record that showed at least some of their customers were aware that the products should only be used for research purposes, because FDA’s own “review of these customers’ websites strongly suggests that these customers are engaged in clinical diagnostic testing.”  RUO certification programs were something that FDA had, at one time, recommended.  In the current RUO Guidance, FDA notes that the existence of an RUO certification program would only be viewed as a factor when assessing the intended use of an RUO product.  Indeed, FDA states, “the existence of a certification program alone would not relieve manufacturers from their responsibilities to ensure that their labeling and distribution practices for RUO/IUO products are consistent with the product’s RUO/IUO label.”  The Warning Letter seems to echo this point.  Importantly, FDA did not say that sales to customers who are doing exclusively clinical diagnostics, alone, formed the basis of the agency’s letter.  These, along with the promotional claims formed FDA’s basis for concluding the products were intended for diagnostic use.

Because LDTs for clinical diagnostic use can sometimes include RUO labeled components, FDA may look to increase its scrutiny of these components as a means of tightening its control of the inputs to LDTs. We do not see the release of this Warning Letter as directly related to the LDT litigation, however.  The DRG Warning Letter cited information gathered in a November 2024 inspection and the warning letter itself was issued the same day as Judge Jordan’s decision in the LDT case.  Therefore, the events surrounding this particular Warning Letter preceded the LDT decision.

That being said, we have no doubt that as the door to regulating LDTs directly has closed, absent new legislation, FDA is likely to look for a new door to open.  Greater scrutiny of RUO products and those companies that manufacture them could be one of those doors.  HPM is keeping a watchful eye on the various indirect means by which FDA may try to regulate LDTs. In a follow-up post, we’ll discuss the different avenues FDA could seek to try to regulate LDTs (or components thereof) without new legislation.  Stay tuned.