knowledge
2021-08-24
What is the difference between an Antigen Rapid Test and an Antibody Rapid Test?
With regard to Covid-19 testing, there is a common misunderstanding between antigen rapid tests and antibody rapid tests – and their applied use. They are both Covid-19 tests, but they differ in their test target, sample methods, timing, and applications of use.
Covid-19 Antigen Rapid Test
The antigen rapid test is a diagnostic tool used to identify if you are currently infected with Covid-19. It tests for the presence of antigens, which are foreign toxins that stimulate an immune response in our body. In the case of Covid-19, the test target is the nucleocapsid phosphoprotein and spike glycoprotein located on the surface of the SARS-CoV-2 virus. The test is normally conducted using a nasal or throat swab specimen and is most accurate in its diagnosis when performed around 5-7 days after exposure to the virus.
Currently, the most common application for use of the Covid-19 antigen rapid test is as a screening tool for regular (every 3-7 days) testing of larger / high-risk populations for early identification of potentially infected individuals and to track the spread of infection within the community. It is also used as a diagnostic tool to test individuals with symptoms, or those who are a close contact of a confirmed case.
Covid-19 Antibody Rapid Test
The antibody rapid test is a diagnostic tool used to identify if you were previously infected with Covid-19 and / or to measure your body’s immune response to a vaccination. It tests for the presence of IgM and IgG antibodies produced by your body in response to a Covid-19 infection and / or vaccination. IgM antibodies serve as a temporary first line of defense and typically start appearing from around 7 days after infection. This is followed by the production of IgG antibodies that serve as a longer-term defense and are the most abundant antibody in our system. They normally appear after 14 days and remain in our bodies for some time thereafter – exactly how long of a period is still unknown at this stage. The test is normally conducted using a finger-prick blood specimen and is most accurate in its diagnosis when performed at least 15 or more days after infection or vaccination.
The primary application for use of the Covid-19 antibody rapid test is to survey prior infection rates in a population, including asymptomatic cases that were previously unidentified – in order to understand the transmission dynamics of the virus in the community, and identify groups at higher risk for infection. Neutralizing antibody tests are also used to measure the body’s immune response to the SARS-CoV-2 virus following vaccination.
| Covid-19 Antigen Rapid Test | Covid-19 Antibody Rapid Test | |
|---|---|---|
| Test Target | Antigens: N/S proteins located on the surface of the SARS-CoV-2 virus. | Antibodies: IgM and IgG produced in response to the SARS-CoV-2 virus. |
| Sample Methods | Nasal or throat swab specimen. | Finger-prick blood specimen. |
| Timing of Test | Ideally 5-7 days after initial exposure to the virus. | Ideally 15+ days post infection or vaccination. |
| Applications for Use | Screening tool for regular testing of high-risk populations for early identification and tracking of infections. Diagnostic tool to test individuals with symptoms, or those who are a close contact of a confirmed case. |
Population surveillance tool to determine prior infection rates. Semi-qualitative test to measure the body’s immune response to the SARS-CoV-2 virus following vaccination. |