How In Vitro Diagnostics Are Regulated in the US and EU

In vitro diagnostics are regulated as medical devices under different instruments in the US and EU: FDA classification and premarket review in America, and the dedicated European Regulation 2017/746 in Europe. The US boundary moved in 2025, when a federal court vacated the FDA's laboratory-developed-test rule and the agency reverted its regulation on September 19, 2025, per FDA's own pages.

What counts as an in vitro diagnostic in the US?

An IVD is a device, under the Federal Food, Drug, and Cosmetic Act, that consists of reagents, instruments or systems intended for use in the diagnosis of disease or other conditions. The regulatory definition in 21 CFR 809.3(a) became the fulcrum of the LDT fight: on May 6, 2024, the FDA issued a final rule amending that definition to add the words including when the manufacturer of these products is a laboratory, per the agency's Laboratory Developed Tests page. That single clause would have pulled tests made and used inside clinical laboratories into FDA device regulation.

The attempt did not survive judicial review. On March 31, 2025, a federal district court vacated that final rule, and on September 19, 2025, the FDA issued a final rule reverting to the text of the regulation as it existed prior to the effective date of the May 2024 final rule, per the same page. The practical result is that laboratory-developed tests sit outside FDA premarket review under the current text, while IVDs manufactured by companies for sale remain fully within it.

Which FDA pathway applies to a marketed IVD?

For tests sold as products, the route to market follows device classification, and the decision sequence is deterministic:

1. Classify the IVD by risk and special controls; most routine chemistry and immunology assays fall in class II.
2. For an IVD with a valid predicate, submit a 510(k) premarket notification demonstrating substantial equivalence.
3. For a novel low-to-moderate-risk IVD without a predicate, request De Novo classification.
4. For high-risk IVDs, including many companion diagnostics, proceed through premarket approval.
5. Sustain compliance with quality-system and postmarket requirements across the product life.

Companion diagnostics illustrate the stakes of pathway choice, because a drug's approved use can be conditioned on a specific test result, tying the test's regulatory status to the drug's label. The quality-system layer changed for everyone on February 2, 2026, when the QMSR took effect, amending 21 CFR Part 820 by incorporating ISO 13485:2016, per the FDA's device program pages. IVD manufacturers are subject to the same quality-system rule as therapeutic-device makers, and the FDA began using its updated inspection process the same day.

What does the EU IVDR require?

Europe runs its own regime under Regulation (EU) 2017/746, which replaced the older IVD directive and has been applicable since May 26, 2022. The regulation imposes conditions on laboratories that develop and use in-house IVDs, a European counterpart to the LDT question that ended differently: rather than exempting in-house tests wholesale, the IVDR allows them only where no equivalent commercial device is available and a set of quality, justification and documentation conditions is met, as analyzed in the peer-reviewed pathology literature.

The EU system also classifies IVDs into risk classes with notified-body involvement for most categories, a structural contrast with the US where the majority of IVDs clear through predicate-based review. A 2023 analysis in the journal Pathologie, examining practical implementation of the regulation's requirements in pathology institutes, describes the conditions the IVDR imposes on in-house IVD development and use; that literature is the reference point for how European laboratories have experienced the transition.

How do the two systems differ where it matters?

The sharpest divergence is now the laboratory test question. The EU chose conditional inclusion: in-house tests are permitted inside a regulated envelope. The US, after the 2024 rule was vacated in court, has returned to a text under which laboratory-developed tests are not FDA-regulated devices, per the agency's September 2025 reversion. Manufacturers selling products in both regions therefore face a notified-body conformity regime in Europe and a classification-based FDA pathway in the US, with separate quality-system obligations that the QMSR has now partially harmonized with the ISO standard European authorities already use.

Timing asymmetry compounds the structural one. A US 510(k) review runs on a statutory decision clock measured in months, while European certification under the IVDR depends on notified-body slot availability as much as on document quality, a constraint laboratories and manufacturers have documented since the regulation became applicable. Programs that sequence the US filing first and EU certification second, or that limit early launches to selected member states, are responding to that calendar reality rather than to any difference in scientific standard.

Postmarket obligations also diverge in emphasis. The FDA's device system leans on inspection, recall authority and the quality-system rule now expressed through the QMSR, while the IVDR builds in periodic safety update reporting, performance follow-up studies for certain devices and economic-operator registration duties across the supply chain. For a diagnostics company, the compliance function is effectively two disciplines run in parallel, and the cost of treating one jurisdiction's habits as universal shows up in review correspondence.

What should manufacturers watch from here?

Three threads are live. First, the LDT question is unresolved rather than settled: the FDA's reversion is a regulatory text change, and any durable framework for laboratory test oversight would now require either new rulemaking on a different legal basis or legislation, neither of which has been enacted. Second, QMSR inspection practice is new: the FDA retired its legacy inspection technique on the February 2026 effective date, per the agency's FAQ page, and early inspection outcomes under Compliance Program 7382.850 will define what compliance looks like in practice. Third, the European transition continues to consume notified-body capacity, which is a scheduling variable for any IVD requiring certification.

For teams planning programs, the checklist is straightforward: classify early in both regions, sequence US pathway selection against EU conformity assessment timelines, and treat the FDA's LDT page and the peer-reviewed IVDR analyses as the checkable anchors for the two boundary questions that moved most recently.