There are currently 3 types of COVID-19 tests available to identify COVID-19 infections. They are the PCR or Polymerase Chain Reaction Test, the Antibody Test, and the Antigen Test, including the Rapid Antigen and At-Home Rapid Antigen Tests.
Please note: These tests are available as of the end of January 2022. Currently, they can detect the original SARS-CoV-2 virus and both the delta and omicron variants. They may or may not be as accurate for any future variants.
COVID-19 tests can cut down infections in the community by identifying people who may be a threat to others and advising them to self-isolate.
Unfortunately, conflicting messages about these tests, along with shifting CDC guidance on quarantine periods, has made it very confusing for people to navigate this stage of the pandemic.
In this article we offer information about the currently available tests—what they are, how they work, and the advantages and disadvantages of each.
What It Is
The PCR or Polymerase Chain Reaction test is the gold standard for detecting the presence of COVID-19 in bodily secretions. It is a molecular test that measures specific genetic material from a virus that has entered the body. The PCR test can identify pathogenic organisms that are difficult to culture by detecting their DNA or RNA and then amplifying it.
How It Works
The PCR test is done by collecting material from the nose or throat using a long swab. The resulting genetic material is sent to a lab to be amplified. The amplification technique is called a polymerase chain reaction (PCR). This process allows the PCR test to detect even the smallest amount of coronavirus genetic material in a sample, making it a highly sensitive and accurate test, approaching an accuracy of 100%.
Advantages of the PCR Test
Disadvantages of the PCR Test
What It Is
The Antibody test is a blood test.
How It Works
Certain foreign substances (called antigens) from either outside the body (such as viruses, chemicals, bacteria, toxins) or inside the body (such as cancer cells) produce an immune response in the form of the production of specific antibodies to those specific antigens. The antibodies bind to those antigens and neutralize them. This knowledge is stored in the immune system’s long-term memory and if the antigen should attempt to attack again, the body will launch antibodies against it.
Material for testing is blood drawn from a finger or an arm and sent to a lab to measure with results available in 1 to 3 days. If the results are positive, a person may have COVID-19 antibodies in their blood with a good chance that COVID-19 had occurred in the past or there was at least exposure.
If the results are negative, there are no COVID-19 antibodies in the blood. Therefore, it may be assumed that the individual has not had COVID-19 in the past, although we do not have enough data to know how long COVID-19 antibodies remain in the body after an infection.
Antibody tests are crucial to understanding how our population may adapt to the virus and how those with antibodies respond to other variants.
The answer is: If a vaccinated individual’s antibody test shows that there are no antibodies to COVID-19 in the body, this should NOT be a sign that the vaccine is not working. Here is why...
What It Is
An antigen test is also known as a ‘lateral flow test.’ Unlike the PCR test, it does not detect genetic material, but can rather identify specific proteins on the surface of the COVID-19 virus.
How It Works
Material for testing is typically obtained by a nasal swab.
Lab-made antibodies search for antigens from the SARS-CoV-2
virus. The antibodies bind to the antigens and the antigen-antibody reaction
produces a colored line on a test strip much like a pregnancy test.
This is COVID-19 test that may be available if a PCR test (which is more accurate) is not readily available. If the result is positive, a person is immediately alerted of the need to self-isolate and to inform contacts of possible infection.
What It Is
The rapid at-home COVID-19 test is an antigen test which can be easily administered by an individual anywhere with results available in fifteen minutes.
How it Works
Material is collected by the individual with a nasal swab.
This test works the same as any antigen test done in a lab but with many obvious advantages of convenience compared to going to a test center or hospital to receive an antigen, PCR or an antibody test with the possibility of long waiting lines at a test center and as many as 3 days’ wait times for results.
1. If a person has been to a gathering and is concerned that someone there may have been shedding virus, but still feels fine.
In this situation it would be best to wait until at least 2 days have passed and then do a rapid test. If it comes back positive, immediately isolate because false positives are rare. To absolutely confirm infection, a PCR test would be in order.
If the rapid test is negative, there may still be an active infection because 15% of the time there will be a false negative. Repeat the test a day or two later. If that is also negative, the chance of infection is small.
The data shows that sequential negative tests come very close to PCR tests in sensitivity (ability to correctly identify everyone with COVID-19 as positive). In fact, when groups of students, employees, or athletes are tested every few days, the rapid tests can identify 98% of infections!
2. If an individual has been in contact with others and is experiencing minor symptoms like coughing, sneezing, sore throat or fever.
The question is whether or not the symptoms are from a cold or the beginning of COVID-19. In this situation, it is best to assume that it is COVID-19 until it can be ruled out.
Once symptoms are present, the sensitivity of the rapid test (its ability to positively identify COVID-19) will be increased.
If the test is indeed positive, then it is very likely that this is not just a cold and the individual should immediately isolate and contact those he or she may have been with.
A PCR test can be obtained to confirm the positive result or the rapid antigen test should be repeated in 2 days. If the result is positive, definitely confirm with a PCR test. If the rapid test is negative, repeat it in 2 days and if it is still negative, then COVID-19 is unlikely.
3. An individual may want to visit an older family member or attend a small gathering.
In this situation, the test should be done just before the event. The reason is that a 2 day old test is unreliable because rapid tests reflect the viral situation only at the time the sample was taken and viral loads can change significantly from day to day.
If the test is positive, the visit should be cancelled, self-isolation should be initiated, and the results should be confirmed with a PCR test.
If the test is negative, it would suggest a low viral load at that point in time and the risk of being infectious is small.
It is important to remember that even though a test is negative, the risk is not zero because an individual may have been in contact with an infected person in the past couple of days and may have acquired the virus, but it has not had enough time to replicate in order to yield a positive test. If this is the case, some of the virus may be able to be passed on, especially if the infection was due to the omicron variant.
Because the omicron variant replicates so quickly, it is possible for a person to be negative when tested just before a gathering, but if the test were to be repeated within a few hours, it might well be positive.
It is also important to remember that there is a 15% chance the test is a false negative in the first place so there is still some risk associated with that possibility.
On the other hand, since life presents us with continuous risk-benefit evaluations and we take some risks all the time, a gathering where everyone has tested negative presents a very small risk.
4. The Ideal Situation
Unless there has been no chance of contact with anyone, the ideal situation would be for people to take a rapid test every few days. This would identify infected individuals who would then isolate and prevent the spread of the virus. Realistically, this is not practical in terms of hassle or cost.
On the other hand, contracting COVID-19 involves a real hassle and high cost. So the most effective way to reduce the spread of the virus is to limit person-to-person contact and to get as many people vaccinated as possible.
1. Do the
Rapid Tests Work for the Different Variants?
Although data is still incoming, the early evidence indicates that the rapid tests work for the original COVID-19 as well as for the delta and omicron variants.
This is because these tests do not involve the spike protein the virus uses to invade a cell but rather look for the virus’ RNA nucleocapsid protein, which is less susceptible to mutations.
With any of the rapid tests, the chance of false
negatives is reduced by repeating the test a couple of days apart.
Of course, there may very well be COVID-19 variants in the future that may necessitate the development of new tests that are sensitive to the new variants.
2. What are the Types of Rapid At-Home COVID-19 tests?
Rapid At-home antigen tests, (for ex. BinaxNow) are available over the counter at a pharmacy (when supplies are available) with results available in under an hour.
Rapid At-home molecular tests (including PCR tests) are generally more accurate than the at-home antigen tests. They detect the genetic material of a virus and work by amplifying any existing genetic material present in a sample, by as much as a billionfold.
These tests can thus detect extremely small amounts of genetic material in a sample making them highly accurate whether or not a person has symptoms. Some of these are available from companies like Cue and Lucira but are pricey and thus not widely accessible to most people.
At-home PCR tests, such as LabCorp’s Pixel are also available, but require mailing the sample to a lab and waiting for a result.
3. Current Cost and Availability of Rapid At-Home COVID-19 Tests
As of January 18, 2022, each household in the US is able to receive 4 free test kits with no shipping costs and no need to enter a credit card number. Click covidtests.gov to order.
The 4 free tests can also be found at the US Postal Service website.
An additional 8 free tests may be available for each household if insurance coverage allows.
Having symptoms of a COVID-19 infection is an important reason to get a COVID-19 test but it is not the only reason. We now know that a person can be infected with COVID-19 and not have any symptoms (asymptomatic).
Thus, it very important to test for COVID-19 (at a test center or at home) 5 to 7 days after a known exposure. If a test is done too soon, a false negative can occur meaning the virus may not have had a chance to produce enough of a presence in your body for the test to detect.
Therefore, a person should consider getting tested if:
IN ANY EVENT…
If you feel you are in need of medical attention or are experiencing a cough, fever, difficulty breathing, sore throat, loss of taste/smell, chills/muscle pain and/or gastrointestinal symptoms, self-isolate and contact your doctor as soon as possible.
With the possibility of future mutations leading to new variants (and as of this writing, a new variant has been spotted), it does not necessarily mean that the pandemic is going to get worse.
The process of natural selection tends to favor viruses that are highly transmissible but not those that are necessarily deadliest.
And, it is important to remember that killing one's host is not always a great strategy for survival!