Testing for viral pathogens has become top-of-mind during the COVID-19 pandemic for many people who wouldn’t normally give it a second thought.
As the virus continues to spread, it’s more important than ever to be aware of the tests used in public health responses to viral outbreaks. In this post, we’ll discuss the different types of tests and how they’re used to detect SARS-CoV-2, the pathogen that causes COVID-19.
What kinds of COVID-19 tests are there?
Broadly, there are two categories of tests: diagnostic and antibody. Diagnostic tests are used to determine if someone currently has an active infection while antibody tests can indicate whether someone has had an infection in the past.
Antibody tests aren’t typically used to diagnose COVID-19 because it can take between one and three weeks after infection for the body to develop antibodies. For this reason, diagnostic tests are used to actively detect the virus in populations and individuals.
- Antigen tests, which detect specific proteins from viral pathogens.
- PCR tests (which stands for polymerase chain reaction), which examine DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) sequences.
How does an antigen test work?
Antigen tests detect the proteins on the surface of a virus. This method is less reliable, but produces much faster results. Antigen tests are great for mass screening of populations because of their speed and cost but negative results may need to be confirmed with a PCR test.
How does a qPCR test work?
Quantitative PCR testing, or qPCR, is the gold standard for COVID-19 testing because of its accuracy. To conduct a qPCR test, a sample is combined with reagents to produce a fluorescent signal. If the target RNA is present in the sample, its concentration eventually reaches the cycle threshold where it’s detected by the fluorescent signal to accurately diagnose a COVID-19 infection.
The result produced by a qPCR test is the most reliable of any diagnostic test for COVID-19 because it can detect very small amounts of the virus.
How and where are these tests used?
The different types of tests each have benefits and drawbacks that make them more suitable for some applications than others.
Environmental testing—the testing of surfaces and wastewater—is done using the PCR method. This ensures a reliable result is achieved when testing for the presence of SARS-CoV-2 in populations or environments.
Diagnostic testing, or testing for individuals, employs a combination of PCR and antigen tests. If you go to a hospital or clinic to get tested for COVID-19, you will most likely receive a qPCR test. Most rapid and popup testing facilities, however, use antigen tests.
What are the differences between qPCR, antigen, and antibody tests?
| Comparison | qPCR Test | Antigen Test | Antibody Test |
| What sample is used in the test? | Most common: Nasal or throat swab Emerging alternatives: Saliva, Saline Rinse | Most common: Nasal or throat swab Emerging alternatives: Saliva, Saline Rinse | Blood sample |
| What does the test measure? | The presence of viral RNA | The presence of viral proteins | The presence of antibodies |
| What does the test determine? | Diagnoses active infection of COVID-19 | Diagnoses active infection of COVID-19 | Shows past infection of COVID-19 |
| How accurate are the test results? | Highly accurate, gold standard method for clinical diagnostics | Accurate positive results but negatives may need to be confirmed with a qPCR test | Possibility for the need of a second antibody test for accurate results |
| How long does it take to get results? | Under 2 hours | Under 1 hour | Under 1 hour |
