What Is an In Vitro Diagnostic (IVD)? A Research-Administration Guide

What Is an In Vitro Diagnostic (IVD)?

An in vitro diagnostic (IVD) is a test performed on a sample taken from the human body — blood, urine, tissue, saliva, or another specimen — rather than on or in the body itself. In vitro literally means “in glass”: the analysis happens in a test tube, cartridge, or instrument outside the patient, not inside a living organism (in vivo). An IVD product is the reagent, instrument, kit, calibrator, or software system used to run that test and interpret the result.

Under U.S. law, IVDs are legally classified as medical devices. The FDA’s own regulatory definition (21 CFR 809.3(a)) describes IVDs as reagents, instruments, and systems intended for use in diagnosing disease or other conditions — including a determination of the state of health — that are “intended for use in the collection, preparation, and examination of specimens taken from the human body.” The EU’s In Vitro Diagnostic Medical Devices Regulation (IVDR, Regulation (EU) 2017/746) uses a similarly broad definition: a medical device that is a reagent, calibrator, control material, kit, instrument, or piece of software intended to examine specimens in order to provide information about a physiological or pathological state, a congenital condition, predisposition to a condition, or to predict or monitor response to treatment.

Practically, the category is enormous. A routine complete blood count, a pregnancy test, a glucose monitor test strip, a PCR assay for an infectious pathogen, a genetic panel, and the software that flags an abnormal result on a lab analyzer are all IVDs.

Why IVDs Are Regulated as a Distinct Category

An incorrect diagnostic result carries real clinical risk even though the product never enters or contacts the patient’s body the way a therapeutic device or drug does — a false negative can delay treatment, a false positive can trigger an unnecessary intervention, and a poorly calibrated instrument can produce systematically wrong results across every patient it tests. Regulators treat IVDs as medical devices specifically because that risk sits in the accuracy and reliability of the result, not in physical contact with the patient. This is why IVD-specific quality requirements exist alongside the general medical-device framework: manufacturing controls, analytical and clinical performance validation, and (for higher-risk tests) independent review before market entry.

IVD vs. Therapeutic Medical Device: What’s the Difference

The distinction that trips people up most often is between an IVD and a therapeutic (or implantable/interventional) medical device. Both are legally “medical devices,” but they do different jobs:

• Therapeutic/interventional medical device — acts on or in the patient to treat, monitor, or support a condition: a pacemaker, an infusion pump, a surgical instrument, a hip implant. Risk is tied to physical interaction with the body.
• In vitro diagnostic (IVD) — never contacts the patient directly; it analyzes a specimen already taken from the patient to produce information used in a diagnostic or treatment decision. Risk is tied to the accuracy of that information.

Because both categories fall under the same underlying device statutes, the general medical-device classification system (device classes, premarket pathways) also applies to IVDs, but IVDs have their own classification rules layered on top — in the EU, IVDR Annex VIII sorts IVDs into Class A through Class D by risk, a different scheme from the general MDR device classes used for therapeutic devices. See What Is a Medical Device? for the broader category IVDs sit inside, and FDA Medical Device Classification for how the risk-class system that also governs many IVDs actually works.

Types of IVDs

IVDs range from equipment sitting in a centralized lab to single-use tests run at the bedside:

• Laboratory-based tests — run on automated analyzers in a clinical or reference laboratory: chemistry panels, hematology, microbiology cultures, molecular diagnostics (PCR, sequencing-based assays). These typically require trained laboratory personnel and centralized instrumentation.
• Point-of-care tests (POCT) — performed near the patient, often with a result in minutes: rapid strep tests, glucose meters, rapid antigen tests, some cardiac-marker assays. Designed for simplicity, sometimes CLIA-waived in the U.S. so they can be run outside a certified laboratory.
• Companion diagnostics — an IVD specifically linked to a particular drug or biologic, used to identify patients likely to benefit from (or be harmed by) that therapy, or to monitor response to it. Because the diagnostic result directly determines treatment eligibility, companion diagnostics are typically co-developed and reviewed alongside the therapeutic product they pair with, and sit at the higher end of the risk classification in both the U.S. and EU frameworks.

How IVDs Are Regulated: FDA and EU IVDR at a Glance

Regulatory oversight varies by risk and by jurisdiction, but the shape is consistent: lower-risk IVDs face lighter requirements, higher-risk IVDs (those a wrong result could seriously harm a patient from, or that involve novel technology) face independent third-party or agency review before they can be marketed.

United States (FDA). Most IVDs are regulated as medical devices under the Federal Food, Drug, and Cosmetic Act, following the same general premarket routes used for other devices — 510(k) clearance for devices substantially equivalent to an already-marketed predicate, De Novo classification for novel low-to-moderate-risk devices with no predicate, or Premarket Approval (PMA) for the highest-risk devices, including most companion diagnostics. Separately, the Clinical Laboratory Improvement Amendments (CLIA) govern who is allowed to run a given test based on its complexity (waived, moderate, or high complexity) — a distinct question from whether the test itself was cleared or approved.

European Union (IVDR). The In Vitro Diagnostic Medical Devices Regulation (EU) 2017/746 replaced the older IVD Directive and, unlike its predecessor, requires independent Notified Body review for most IVDs rather than manufacturer self-certification — a major shift, since the large majority of IVDs were self-certified under the old directive. IVDR sorts devices into Class A (lowest risk) through Class D (highest risk, e.g. tests for transmissible agents in blood/tissue donations) under Annex VIII, with review requirements scaling accordingly.

This page is deliberately a summary. For the full classification rules, Notified Body process, and the phased transition deadlines that are still actively rolling out under IVDR, see the deep-dive guide: IVDR (EU 2017/746): Classification, Notified Body Requirements, and Transition Deadlines.

Why This Matters for a Research Organization

IVDs show up across several roles in a research-administration context, not just in a clinical lab:

• Regulatory affairs / compliance staff handling submissions or vendor qualification for any study that uses a diagnostic test as an inclusion criterion, endpoint, or companion diagnostic.
• IRB/ethics coordinators reviewing protocols where an investigational IVD is used to screen, stratify, or monitor participants — the diagnostic itself may carry its own regulatory status separate from the drug or intervention under study.
• Lab managers and quality staff maintaining CLIA certification, instrument calibration, and validation records for IVDs used in-house.
• Procurement and equipment managers sourcing the instruments and consumables an IVD workflow depends on — specimen collection and handling supplies, laboratory filtration used in sample prep, and the analyzers or monitoring equipment a test runs on. See Specimen Collection Kit Standardization for Multi-Site Clinical Trials, Clinical and Laboratory Filter Selection Guide, and Choosing Diagnostic and Patient Monitoring Equipment: A Procurement Guide for the procurement side of running IVD-dependent testing.

Go Deeper on CASRAI

This page is an entry point. CASRAI’s device-and-diagnostics coverage goes considerably further into the specific regulatory mechanics:

• Medical Device & Diagnostics Quality — the subcluster hub covering ISO 13485, design controls, IVDR, pharmacovigilance, and regulatory affairs for device and diagnostics work.
• IVDR (EU 2017/746): Classification, Notified Body Requirements, and Transition Deadlines — the full classification and transition detail summarized above.
• FDA Medical Device Classification and What Is FDA 510(k) Clearance? — the U.S. pathway most IVDs go through.

Frequently Asked Questions

Is an IVD the same thing as a medical device?

An IVD is a medical device under U.S. and EU law, but not every medical device is an IVD. IVDs are the subset of medical devices used to analyze specimens outside the body; devices that act on or in the patient directly (implants, surgical tools, infusion pumps) are medical devices but not IVDs.

What is a companion diagnostic?

A companion diagnostic is an IVD used to determine whether a patient is an appropriate candidate for a specific drug or biologic therapy, or to monitor their response to it. Because the result directly gates treatment eligibility, companion diagnostics are usually developed and reviewed alongside the therapeutic product itself.

Does the FDA regulate at-home tests the same way as lab tests?

At-home and point-of-care tests are still IVDs and go through the same general classification and premarket framework, but they’re typically designed and validated for use by an untrained operator, and many are CLIA-waived so they can legally be run outside a certified laboratory.

Who at a research institution needs to know about IVD regulation?

Anyone involved in a study that uses a diagnostic test as part of the protocol — regulatory affairs and compliance staff handling submissions, IRB coordinators reviewing protocols that use investigational diagnostics, lab managers maintaining CLIA certification and validation records, and procurement staff sourcing the instruments and consumables the testing depends on.