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What are rapid COVID-19 tests?
COVID-19 tests come in a few variations. Molecular tests, which include PCR tests and antigen tests, many of which are rapid antigen tests, are the two common diagnostic tests, meaning they identify current infections and infections from the recent past. Antibody tests are also common, detecting antibodies that may suggest you had the virus in the past, but antibody tests should not be used to identify current infections. Research is still underway to determine the role of antibodies in COVID-19 infections.
Rapid antigen tests look for unique proteins that are specifically found on the surface of the SARS-CoV-2 virus. These proteins are known as antigens, and they are what normally signal the immune system to produce antibodies. On the other hand, molecular tests detect the genetic material of the coronavirus, oftentimes through a process known as polymerase chain reaction (PCR).
Many antigen tests got the “rapid test” label because the results came so quickly. Samples could be processed within minutes, giving patients results within 15 to 30 minutes. By comparison, most PCR test samples have to be sent to a lab for processing, and depending on the lab’s workload, it may take a few days to see your results. The FDA approved the use of a rapid PCR test, which uses the same genetic test but with quicker results. For the sake of this article, “rapid test” refers to the antigen tests.
The process of obtaining a sample is typically the same for rapid tests and molecular tests. Many of these diagnostic test require an upper respiratory sample, such as a nasopharygeal swab or anterior nasal swab specimen. The swab is inserted a few inches through a nostril (depth of insertion depends on the sample type), twisted, and then removed. The process can tickle and make you sneeze after, and reaching the nasopharynx requires going deep into the nostrils, which can feel uncomfortable.
Some tests may also use a saliva sample. It can take a great deal of spit, which some people, have trouble producing.
Once the sample has been collected, it is processed to determine the potential presence of SARS-CoV-2. You will usually receive your test results within 15-30 minutes when taking a rapid antigen test.
Advantages of Rapid Testing
The biggest advantage of rapid testing is in the name: these tests offer results quickly and efficiently. The virus can progress at a rapid rate, so getting your test results within minutes versus a few days can make a huge difference in your health and your ability to prevent the spread of the virus to others in your community.
Much of that comes down to the ease of use. They are more affordable and less clunky than molecular tests. Rapid tests can be performed at the point of care, meaning in a healthcare provider’s office, clinic, or emergency room. There are several at-home collection kits, like the OnGo/CareStart Antigen Self-Test that allows you to collect a sample from the comfort of your home.
Accuracy of Rapid Tests
A potential disadvantage of rapid tests is that they are generally regarded to have lower sensitivity than laboratory-based molecular tests. Granted, no test, not even the molecular test, is accurate 100 percent of the time. There are many factors at play. So how common are false positive rapid COVID-19 tests? How about false negatives?
A false positive means that your results show a positive test even though you don’t actually have a COVID-19 infection. There is a chance that any test can give you a false positive result. If you have any doubt about your rapid antigen test result, it is recommended to discuss your results with a healthcare professional to determine next steps which may involve a confirmatory PCR test.
The percent of positive test results that are true positives (also known as Positive Predictive Value or PPV) varies with how common infection is in a population. As the number of infections in the community decreases, the number of test results that are false positives increases. Therefore when numbers of infections are low (low prevalence), false positive results may be more likely than true positive results.
It is possible for any test, including rapid antigen tests, to give a negative result that is incorrect (a false negative result). Much of this comes down to the sensitivity of the test. While molecular tests have a lower limit of detection, meaning they can detect smaller amounts of virus, antigen tests require much higher viral loads.
Lower viral loads usually occur at the beginning of infection or towards the tail-end of an infection’s course. Specimens collected from people who do not have symptoms of COVID-19 are thought to more likely be a false negative compared to people who do have symptoms of COVID-19. If your results from a rapid test come back negative, but you are experiencing symptoms of COVID-19, it is recommended to seek medical attention.
If your results from a rapid antigen test come back negative and you are not experiencing symptoms, your healthcare provider may recommend taking the test again a few days later, when the viral load may have increased. Alternatively, the healthcare provider may recommend taking a PCR test to confirm the results.
When to get tested
With the distribution of vaccinations, knowing when to get tested can be confusing for many people. You should get tested if you:
- Exhibit any symptoms of COVID-19
- Have been in close contact with someone exhibiting COVID-19 symptoms or with confirmed COVID-19 (unless you have been fully vaccinated or had the disease within the last three months)
- Have taken part in any activities that have put you at high risk of COVID-19 (travel, being in a crowded indoor setting, attending a large social gathering) and have not been fully vaccinated or have not had COVID-19 within the last three months
- Are asked to get tested by your healthcare provider or a public health official
Regardless of vaccination status or prior infections, if you experience any signs or symptoms of COVID-19, you should self-isolate and speak with your healthcare provider to determine if you should get tested for SARS-CoV-2.