An IVD, or in vitro diagnostic, is a medical test performed on a sample taken from the human body, such as blood, urine, or tissue, to detect diseases, monitor health conditions, or guide treatment decisions. The term “in vitro” literally means “in glass,” referring to the fact that these tests happen outside the body, typically in a lab setting. IVDs are one of the most widely used tools in modern medicine, with laboratory testing playing a role in roughly two-thirds to three-quarters of all clinical decisions.
How IVDs Work
The basic concept is straightforward: a healthcare provider collects a sample from your body, and that sample is analyzed using specialized reagents, instruments, or both. The results tell your doctor something meaningful about your health. A pregnancy test, a blood glucose monitor, a COVID-19 rapid test, and a cholesterol panel are all IVDs. So is the complex genetic sequencing that identifies whether a tumor carries a specific mutation.
An IVD system typically includes several components working together. Reagents are the chemical substances that react with your sample to produce a measurable result. Instruments are the machines that read and process those reactions. Software interprets the data, flags abnormal values, and can even block results that fail quality checks. Calibration materials and controls ensure the system produces accurate, consistent readings from one test to the next.
Types of IVD Technology
IVDs span a wide range of scientific methods, but most fall into a few major categories:
- Clinical chemistry tests measure substances like glucose, electrolytes, and cholesterol in your blood or urine. These are the workhorses of routine checkups and hospital labs.
- Immunoassays detect specific proteins or antibodies using immune-system-based reactions. Hormone tests, allergy panels, and many infectious disease tests rely on this approach.
- Molecular diagnostics analyze DNA, RNA, or other genetic material. PCR-based COVID tests are a well-known example, but this category also covers genetic screening, pathogen identification, and tumor profiling.
These categories overlap in practice, and newer platforms combine multiple approaches on a single instrument.
Lab-Based Testing vs. Point-of-Care Testing
Most IVDs run in centralized laboratories, where large automated analyzers process hundreds or thousands of samples per day. Results from these labs can take hours to days depending on the test.
Point-of-care testing (POCT) brings the IVD directly to the patient. These are simpler, often portable devices used in emergency rooms, clinics, pharmacies, or even at home. A fingerstick blood sugar meter and a rapid strep test both qualify. The defining advantage is speed: point-of-care tests typically deliver results in minutes rather than hours, which can be critical when treatment decisions need to happen fast. The tradeoff is that point-of-care devices generally handle a narrower range of tests and may be slightly less precise than their full-lab counterparts.
Companion Diagnostics
A specialized subset of IVDs called companion diagnostics (often abbreviated CDx) helps doctors match patients to the right drug therapy. These tests identify whether you carry a specific genetic marker or protein that predicts how you’ll respond to a particular medication. A companion diagnostic might determine whether a cancer drug is likely to work for your specific tumor type, whether you’re at higher risk for serious side effects from a therapy, or whether your body is responding to an ongoing treatment.
The FDA considers companion diagnostics essential for the safe and effective use of their paired drugs. In many cases, a doctor cannot prescribe the drug without first running the companion test.
How IVDs Are Regulated
In the United States, IVDs are regulated as medical devices under the Federal Food, Drug, and Cosmetic Act. The FDA defines them as “reagents, instruments, and systems intended for use in the diagnosis of disease or other conditions, including a determination of the state of health.” This covers everything from a simple test strip to a multimillion-dollar automated laboratory system.
IVDs are classified into risk-based tiers. Low-risk devices face the fewest regulatory requirements, while high-risk devices (those where an incorrect result could lead to serious harm) require the most extensive review before they can be sold. A basic urine dipstick faces a different level of scrutiny than a genetic test used to guide cancer treatment.
Laboratory Developed Tests
One important distinction in the IVD world is between commercially manufactured tests and laboratory developed tests (LDTs). An LDT is an IVD that is designed, made, and used entirely within a single laboratory rather than sold as a product. Hospitals and academic medical centers have long created their own tests for conditions where no commercial option exists.
Historically, LDTs operated under limited FDA oversight. That changed in April 2024, when the FDA issued a final rule clarifying that IVDs are regulated devices regardless of whether the manufacturer is a commercial company or a laboratory. The agency outlined a four-year phaseout of its previous hands-off approach, meaning that over time, lab-created tests will generally need to meet the same requirements as commercially distributed IVDs.
Why IVDs Matter
The global IVD market was valued at roughly $106 billion in 2025 and is projected to grow to about $128 billion by 2033. That scale reflects just how central these tests are to healthcare. A 2016 study of oncologists and cardiologists found that 75% of all their patients underwent laboratory testing, and that testing led to a meaningful clinical decision in 66% of those patients. For cardiovascular disease alone, clinical guidelines recommend some form of laboratory testing in an average of 77% of their individual recommendations.
For patients, IVDs are often the invisible infrastructure behind a diagnosis. You may never think about the technology that processed your blood sample, but the result it delivers can determine whether you start a medication, undergo surgery, or simply get reassurance that everything looks normal.