in vitro
Meaning of in vitro: A label recording where a result came from, and a standing warning that a dish is a far simpler place than a body.
Definition of in vitro
In vitro describes something done outside a living organism, in a test tube, culture dish or other controlled laboratory setting. The phrase is attached to a result to say where it was produced, since an effect seen on cells in a dish was observed under conditions the experimenter controlled rather than inside a working body. Its counterpart is in vivo.
How do the related terms compare?
| Term | Where the work happens | Typical example |
|---|---|---|
| In vitro | Outside the organism, in a dish or tube | A drug tested against bacteria in culture |
| In vivo | Inside a living organism | The same drug given to an animal or a person |
| Ex vivo | On tissue removed from a body, often returned afterward | Immune cells modified in a laboratory before being given back |
| In silico | In a computer simulation | Predicting how a molecule binds before any is made |
The sequence is usually deliberate. A question is answered first where conditions can be held constant, cheaply and quickly, before anything is tried in a living system. Work in a dish allows one variable to be changed at a time, permits far more conditions to be tested than any animal or human study could accommodate, and avoids exposing anyone to a compound that turns out to do nothing.
Why does a result not always carry over?
Because the body adds back everything the dish left out. A compound that kills cells in a flask may never reach the equivalent concentration in tissue, may be broken down by the liver before it arrives, may not cross into the organ it needs to reach, or may harm healthy cells just as readily once loose in a person. Cells grown in a flask also change, adapting to a flat surface, an artificial fluid, and the absence of the neighboring cell types and immune signals that surround them in real tissue. This gap is why most compounds active in a dish never become medicines, and why a laboratory finding is described as promising rather than proven.
Where does the phrase turn up in clinical use?
The best known instance is in vitro fertilization, named because egg and sperm are brought together in the laboratory and the resulting embryo transferred afterward. The phrase also names a whole category of testing. An in vitro diagnostic is any laboratory test performed on a sample taken from the body, such as blood, urine or tissue, as opposed to a measurement made on the person directly. Regulators treat that category separately from devices used on a patient, so the Latin phrase carries real weight in how a product is approved and labeled.
Used in a sentence
The compound showed activity against the bacteria in vitro, prompting further study in animal models.
Good to know
A finding observed in vitro does not automatically apply in vivo, since a controlled laboratory environment can behave differently from the more complex conditions present within a living body.
Word origin
Where “in vitro” comes from
Formed from Latin in vitro, meaning in glass, referring to the glass laboratory vessels traditionally used for such experiments.