Testing for COVID 19 using RT PCR
What
is a PCR test?
A polymerase chain reaction (PCR) test is
performed to detect genetic material from a specific organism, such as a virus.
The test detects the presence of a virus if you are infected at the time of the
test. The test could also detect fragments of the virus even after you are no
longer infected.
What
is a COVID-19 PCR test?
A PCR test for COVID-19 is a test used to
diagnose people who are currently infected with SARS-CoV-2, which is the
coronavirus that causes COVID-19. The PCR test is the “gold standard” test for
diagnosing COVID-19 because it’s the most accurate and reliable test.
Who
should get tested for COVID-19?
Get tested:
- If you have symptoms of
COVID-19.
- If you have been within six feet of someone
for 15 minutes or more who has tested
positive for Covid-19. (Note: some testing sites don’t offer testing if
you’ve been exposed but don’t have symptoms.)
TEST DETAILS
How
does a COVID-19 PCR test work?
There are three key steps to the COVID-19
PCR test: 1) sample collection, 2) extraction, and 3) PCR.
1. Sample
collection is done using a swab to collect respiratory material found in your
nose. A swab contains a soft tip on a long, flexible stick that is inserted
into your nose. There are different types of nose swabs including nasal swabs
that collect a sample immediately inside your nostrils and nasopharyngeal swabs
that go further into the nasal cavity for collection. Either type of swab is
sufficient for collecting material for the COVID-19 PCR test. After collection,
the swab is sealed in a tube and then sent to a laboratory.
2. When
a laboratory technologist receives the sample, they perform a process called
extraction, which isolates genetic material from the sample including genetic
material from any virus that may be present.
3. The
PCR step then uses special chemicals and a PCR machine called a thermal cycler,
which causes a reaction to occur that makes millions of copies of a small
portion of the SARS-CoV-2 virus’s genetic material. During this process, one of
the chemicals produces a fluorescent light if SARS-CoV-2 is present in the
sample. This fluorescent light is a “signal” that is detected by the PCR
machine and special software is used to interpret the signal as a positive test
result.
RESULTS AND FOLLOW-UP
What
do COVID-19 PCR test results mean?
A positive test result means
that it is very likely that you have COVID-19. Most people have mild illnesses
and can recover safely at home without medical care. Contact your healthcare
provider if your symptoms get worse or if you have questions or concerns.
A negative test result means
you probably didn't have COVID-19 at the time you took your test. However, it
is possible to be infected with SARS-CoV-2 but not have enough virus in your
body to be detected by the test. For example, this may happen if you recently
became infected but you don’t have symptoms, yet; or it could happen if you've
had COVID-19 for more than a week before being tested. Keep in mind that a
negative test doesn’t mean you are safe for any length of time. You can be
exposed to COVID-19 after your test, get infected and spread the SARS-Cov-2
virus to others.
If your test is positive, talk with your
healthcare provider, stay home and separate yourself from others. If your test
is negative, continue to take steps to protect yourself and others from getting
COVID-19. Read more about what to do if you test
positive and ways to prevent getting infected with COVID-19.
How
soon are results of a COVID-19 PCR test available?
You should receive the results of your test
as early as 24 hours after sample collection, but sometimes it can take a few
days depending on long it takes the sample to reach the laboratory and how many
other samples are in the queue to be tested.
What
are the advantages of a COVID-19 PCR test?
The main advantages of the COVID-19 PCR test
are its accuracy and reliability. It is the most accurate test available for
COVID-19 detection.
Are
there downsides to a COVID-19 PCR test?
Because the test is able to detect very
small amounts of virus material, it can continue to detect fragments of The SARS-CoV-2 virus even after you’ve recovered from COVID-19 and are no longer
contagious. So you may continue to test positive if you have had COVID-19 in
the distant past, even though you can’t spread the SARS-CoV-2 virus to others.
ADDITIONAL DETAILS
How
does the COVID-19 PCR test compare with other available COVID-19 tests?
Basically, there are two types of tests,
diagnostic tests and antibody tests. Diagnostic tests tell you if you have an
active (current) COVID-19 infection. Antibody tests tell you that you already
had COVID-19.
Diagnostic
tests:
- PCR test: This tests for
the presence of the actual virus’s genetic material or its fragments as it
breaks down. This is the most reliable and accurate test for detecting
active infection.
- Antigen test: This test detects bits of proteins on the surface of the virus called antigens.
Antigen tests are typically considered rapid, taking only 15 to 30 minutes but are less accurate than a PCR test. Rapid antigen tests are most accurate when used within a few days of the start of your symptoms, which is when the largest amount of virus is present in your body. Because this test is not as accurate as a PCR test, if an antigen test is negative, healthcare providers may order a PCR test to confirm the negative test result.
Antibody
test:
- Antibody (serology) test: This tests detects if you’ve had an immune response (antibodies)
to the virus. This means that you’ve had the virus and your body (immune
system, specifically antibodies) has mounted an attack to fight it. The
test is detecting those antibodies. It typically takes about a week after
being infected for enough antibodies to develop to be detected in your
blood. For this reason, this test shouldn’t be used to diagnose an active
infection.
Video Credit: Teacher - Khan Sir
