A guide to COVID-19 tests for the public
To comprehend testing procedures, it is necessary to comprehend the structure of the coronavirus SARS-CoV-2, which produces COVID-19. The virus is made up of a core of nucleic acid (nucleic acids make up the genetic code of the virus) in the form of RNA, surrounded by a coat called the envelope, which is constructed of different proteins. Extending from the envelope are spikes composed of a protein termed S (spike). Attaching to cells of the human respiratory tract is the S protein.
Commonly available SARS-CoV-2 assays can detect either:
- RNA identified by the PCR assay
- encircling proteins identified by fast lateral flow devices
- antibody testing detects the human body’s immune reaction to the infection.
PCR TESTING NUCLEIC ACIDS ARE WHAT MAKES UP THE VIRUS’S GENETIC CODE
PCR tests detect the RNA of a virus. These tests are often performed in a laboratory using a nasal and/or throat swab. PCR tests may identify incredibly little amounts of RNA, indicating that they are highly sensitive. They are the greatest way to detect an active infection.
Patients infected with COVID-19 typically test positive for PCR a day or two before the onset of symptoms and continue to test positive for some time after that. Once a diagnosis has been made, it is not required to repeat PCR.
The isolation period is determined by the time between the onset of symptoms or, in the absence of symptoms, the first positive test. The current protocol in the United Kingdom requires patients to self-isolate for ten days afterward.
WHEN SHOULD I SUBMIT TO A PCR TEST?
If you are experiencing symptoms that could be indicative of COVID-19, this is the test you should have to diagnose the infection.
Suppose a test for lateral flow is positive. The goal of the PCR test, which is more accurate than the lateral flow test, is to confirm the diagnosis.
IS A PCR TEST RELIABLE?
PCR is the most precise test available for detecting active infections. A positive PCR test will likely indicate an infection in a patient with symptoms. If a person exhibits signs of illness, but a PCR test is negative, doctors may repeat the test if they continue to suspect infection (e.g., in hospitalized patients).
LATERAL FLOW TESTS
These are the commonly utilized quick tests in the community. They are convenient because they provide results in thirty minutes and do not require a laboratory.
Detect the virus’ proteins, not its RNA. They utilize a nasal and throat swab and are performed on a compact, flat plastic device similar to a pregnancy test. These assays differ greatly from PCR. They are not suitable for diagnosing individual people who have symptoms and suspect they may be infected.
Patients with symptoms require a PCR test. Lateral flow tests are designed to detect extra infected individuals who might otherwise be missed due to the absence of symptoms.
WHEN IS A LATERAL FLOW TEST NECESSARY?
You should only do this test if you are symptom-free and have been invited to do so as part of an exercise to identify asymptomatic carriers.
ACCURACY OF LATERAL FLOW TESTS
These assays lack the sensitivity of PCR. They are merely a convenient method of identifying a fraction of undiagnosed individuals with no symptoms. The way to view these tests is that each additional positive result is a plus, avoiding the spread of the virus in unforeseen ways.
If a person has a positive result from these tests, they must confirm it with a more accurate PCR. In the interim, they must separate themselves.
If these tests are negative, the individual may or may not be infected and must continue to take the standard measures, including d washing, mask use, and social isolation.
A negative lateral flow test should not be used to rule out infection or indicate that it is safe to visit family.
Here you can learn more about the precision of lateral flow tests.
These tests detect the body’s response to a previous illness by searching for antibodies produced by the body.
It takes time for the body to generate antibodies after infection. Therefore, antibody testing cannot be used to diagnose individuals at the time they exhibit symptoms. They are useful for determining whether a person was infected in the past. This is important for analyzing, for instance, the number of infected individuals in a population.
It is unknown how long antibody tests remain positive following an infection. Antibody concentrations are expected to diminish over months or years.
WHEN SHOULD I HAVE AN ANTIBODY TEST?
To determine how many people have been affected in the past, you may be required to undergo an antibody test.
In the future, if a physician wanted to determine whether you had been infected in the past, they might conduct an antibody test.
Limitations of COVID-19 testing
No test is 100 percent reliable, not even ones that fulfill regulatory performance and safety standards. Additionally, the results are only applicable to that sample at that moment.
Suppose you are uncertain about what a test result means or what you should or should not do after receiving your test result. In that case, you should first contact the test provider, and if you are still uncertain, you should speak with your primary care physician or another healthcare professional.
It is essential to comprehend the limitations of COVID-19 tests, as an incorrect or incorrectly interpreted result can provide a false sense of security. For instance, if you are infected with the virus but the test you take generates a false negative result (it indicates you do not have the virus when you do), you may spread the virus unintentionally to others or fail to seek the treatment you may require
Antibody testing, in particular, has limits, mainly because we do not yet know much about COVID-19 immunity. For instance, we do not yet know if:
- Antibodies prevent subsequent infection with COVID-19.
- Antibodies prevent the transmission of the virus.
- Negative antibody results indicate that you have never been infected.
- The reliability (also referred to as “sensitivity”) of the test can be found on the label or in the instructions for the testing kit.