Chances are, you already know what an assay is—if you’ve ever used a pregnancy test or a rapid result COVID test, you’re more than familiar with fast results that seem to appear in front of you like magic.
What is an assay? How do they work? Don’t let their simplicity fool you; they’re actually one of the most powerful probing tools of exploration whenever more information about a person, a biochemical system, a plant, an animal, or anything else is required.
What is an assay? Definition, meaning, and purpose
The primary goal of a medical assay is to determine whether or not a fluid or tissue sample contains a target analyte—in our case, SARS-CoV-2, AKA COVID-19. How?
Reagents are used to reveal the presence of any target, affording us an up-close-and-personal glimpse into the biophysical profile of anything from blood or saliva to a sample of water from a river.
Reagents can be described as any compound, chemical, or process designed to interact with the target analyte recognizably. They’re used to determine the presence or validity of a number of different pathogens, conditions, or even things like narcotics or specific types of food.
Absorbance, fluorescence, luminescence, radioactivity, and more can all be used to learn more about a specimen that’s been exposed to the assay, bridging the gap between the microscopic and the visible, tangible world around us.
A positive indication is called a “hit”—the specificity of the assay refers to the likelihood of the test delivering a false positive, and the sensitivity describes the baseline starting conditions under which the test can be used successfully.
Different types of assays
Not all assays are exactly the same. The identity of the target analyte will be one factor influencing the type of assay that might be best for the task, but there are also others to consider.
Biochemical assays vs. cell-based assays
In a general sense, most medical assay tests can be classified as being either cell-free biochemical assays or cell-based assays, such as the type used to detect the presence of COVID-19.
Depending on the goals of the test, biochemical assays may be able to render biologically relevant results beyond the world of the strictly animate. Assays designed to test the chemical content of rainfall, for example, may provide valuable insight into the health and the future of the biome that relies on it.
In vitro and in vivo assays
Biological assays can be broken down further into two new major categories: in vitro and in vivo assays. In vivo means within the organism, while in vitro refers to lab work done in a test tube.
Both have their place in the scientific community; in vivo assays, for example, may be preferred when a biologist would like insight into how one single mechanism of action informs whole-animal metabolism, or perhaps the behavior of other, interrelated systems within the body.
Any of the commercially-available COVID tests at your disposal are in vitro assays, not in vivo. When only one target analyte is on the table, the convenience and simplicity of an in vitro assay will usually be the test of choice used to answer a simple yes-or-no question—EG, do I have COVID-19?
What else can an assay be used for?
Some of the other ways that doctors, forensic specialists, and even just ordinary people use assays may also include the following:
- Pregnancy tests
- Drug discovery
- Cell viability
- Cancer diagnosis
- And, of course, for the detection of pathogens like COVID-19
For assistance with the latter, Covid Clinic always has your back. To learn more about COVID-19 testing near you, please feel free to get in touch.