There are three types of COVID-19 tests available:
PCR vs Antigen Tests
What are the most common types of COVID-19 tests?
Antigen
These tests detect antigens: pieces of a virus that the immune system recognizes. A single virus has many antigens. These tests tell if you are infected now.
Molecular
Molecular tests detect genetic material from the virus. A series of chemical reactions copies viral genetic material. These tests tell if you are infected now.
Antibody
These tests detect antibodies: Y-shaped molecules made by the immune response to disable a virus or mark it for destruction. These tests tell if you were possibly infected in the past.
An antigen test looks for surface proteins from the coronavirus infection. When tested, these react with a reagent to give a positive or negative result.
The term NAAT test is often interchangeable with PCR, as the reverse transcription-polymerase chain reaction is the preferred approach to detecting coronavirus. NAATs also cover other amplification techniques for detecting small amounts of viral RNA. Antibody testing requires a blood sample and detects antibodies resulting from infection. Antibodies are a historical indicator of disease and remain in your bloodstream for several months.
Antigen Tests
The antigen test for COVID-19, commonly known as a rapid test or a lateral flow test, is a straightforward test that gives a result in minutes and is also available as a home test kit.
What is an Antigen Test?
The antigen test relies on a chemical reagent reacting with pieces of coronavirus proteins in the sample. Like a pregnancy test, you get a visual indication (typically two lines) showing a positive or a negative test result. The antigen test requires high levels of the virus protein in the test sample; otherwise, you get a false negative. The antigen test reassures you that you don’t have the virus, but you may still be in the early stages of infection.
How Is the Sample Taken?
The typical sample for a COVID-19 antigen test is a taken from the nose, mouth, or both using a swab. Some antigen tests can use saliva or blood but the best sample for an antigen test is from the nose with an anterior nasal swab that doesn’t require a health professional.
Nose Nasal Swab Test
Mouth Nasal Swab Test
Saliva Test
Blood Test
For an anterior nasal swab COVID-19 test, you insert the swab less than three-quarters of an inch into the nostril and swirl it at least four times to collect sufficient material for the test.
How Accurate are the Results?
Studies of antigen tests on people with known coronavirus infections show that antigen tests successfully report a positive test result in 72% of cases with symptoms and only 58% of those without symptoms.
Antigen tests work best when people already have symptoms and a correspondingly high viral load. Sensitivity varies but is always less than laboratory-based PCR tests.
You may test negative with an antigen test during these periods but can still infect other people.
PCR Tests
A PCR test detects the active COVID-19 virus and is the best diagnostic tool for confirming a person has coronavirus and is infectious.
What is a PCR Test?
A PCR test uses laboratory equipment and a cycle of reactions with chemicals, enzymes, and heat to convert the RNA (ribonucleic acid) into DNA (deoxyribonucleic acid) and boost the quantity to a detectable amount. As soon as the virus DNA level reaches the target amount, a chemical is added that causes there to be a flash of light discernible by the PCR machine. After a specified number of cycles, if there is no light there is no virus present in the sample. A high level of COVID-19 means fewer heating and cooling cycles to achieve a positive result, or the amount present is insufficient to cause an active infection.
How Is the Sample Taken?
A professional will collect the sample using a nasal or a mouth swab or you can collect the sample yourself. Some PCR machines can test saliva samples, which are less invasive and more convenient for everyone. A COVID-19 saliva PCR test is suitable for pool and individual testing.
Most sampling techniques use a swab from the mouth and the nose but with less penetration. The best sample involves a deep nasal swab, but this is difficult for people to self-administer without damage. The nasal swab COVID-19 test is the choice of most medical professionals.
How Accurate are the Results?
A PCR test is less likely to give false-negative results. Trials of PCR tests indicate that they are 94-99% accurate in confirming the presence or absence of COVID-19.
Although you can get false positives (a positive test result when you don’t have the virus) and false negatives (a negative test result when you do have the virus) with any test, the rate of these is substantially lower with a PCR Test.
Pros
The advantages include:
• More sensitive, captures asymptomatic carriers and individuals
in the early stages of infection.
• Clearly indicates if someone is infectious.
• A negative result clears an individual as being noninfectious.
• Acceptable for travel and diagnostic purposes.
• Suitable for screening and surveillance to help catch
asymptomatic carriers of the virus.
• Suitable for pool and pod testing – helps lower cost.
Why Chose PCR instead of Antigen Testing?
Although an antigen test promises the reassurance of a quick test you can do at home, most health professionals say that a negative antigen test does not clear you to go about daily life confident that you do not carry coronavirus.
Antigen testing is only accurate when you already have an abundance of the virus in your system. It performs poorly during the early stages and when you are asymptomatic. Antigen testing gives you the false reassurance that you are not infectious, whereas a PCR test is sensitive at all stages of infection. PCR testing gives you a defined end to the infectious period, whereas antigen tests cannot currently provide this reassurance.
The main benefit of using PCR testing over antigen testing is the confidence that you are receiving the correct result and are clear from spreading the virus. That’s why PCR is the gold standard.
