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How Is Coronavirus Detected in Patients with Covid-19?

Jul. 20, 2021

Currently, the U.S. Food and Drug Administration (FDA) has approved two types of diagnostic tests to diagnose COVID-19: molecular tests and antigen tests. In molecular testing, the polymerase chain reaction (PCR) is used to detect viral genetic material. The test is performed using a biological fluid collected from a nasal or throat swab or saliva. Some home test kits, such as nasal swab kits and saliva kits, are also effective in detecting coronaviruses.    

In antigen testing, biological samples collected from nasal or throat swabs are used to detect certain viral proteins. Compared to molecular tests, antigen testing is less sensitive and less accurate because of the possibility of obtaining false negative results.

The novel coronavirus antibody detection kit is used for rapid qualitative detection of novel coronavirus IgM/IgG antibody in human whole blood, serum and plasma. The detection results can be obtained by visual observation within 15 minutes at the earliest.

What is a coronavirus antibody test?

Antibodies are produced by the immune system to recognize and destroy harmful foreign substances (antigens), such as bacteria and viruses. A coronavirus antibody test is performed to detect the presence of antibodies produced against the coronavirus in the blood. A positive coronavirus antibody test may mean that a person was infected with a coronavirus at some point in the past. However, a positive result does not indicate that a person is currently infected with the coronavirus.

 Novel Coronavirus Antibody Detection Kit

Novel Coronavirus Antibody Detection Kit

How does the coronavirus antibody test work?

For SARS-CoV-2, detectable antibody levels in the blood can be reached 1-2 weeks after infection. The basic approach to coronavirus antibody testing involves examining the binding of a targeted antibody to a specific viral protein (antigen). Platforms used to perform coronavirus antibody testing include enzyme-linked immunosorbent assays ( ELISA ), chemiluminescent immunoassays, and lateral flow assays.


To perform the test, a blood sample is collected and incubated with the viral antigen on the assay platform. If an antibody against the coronavirus is present in the blood, it binds to the viral antigen, resulting in a positive result.

The viral antigens used to detect antibodies to coronaviruses include spinosin (a specific surface protein that binds to host cells and facilitates viral entry), nucleocapsid (an RNA-binding protein used to form the viral capsid) and receptor-binding domain (part of the spinosin protein that binds to the coronavirus host receptor, known as angiotensin-converting enzyme 2 ( ACE2 )).


The types of antibodies detected by antibody testing include IgM (usually the first antibody produced at the time of infection), IgG (the most abundant antibody in the blood) and IgA (protects the mucosa). Total antibody levels can also be measured.    


What are the benefits and limitations of coronavirus antibody testing?

If a person tests positive on an antibody test but has no symptoms associated with the disease, the likelihood of current infection is low. However, a negative antibody test result does not exclude the possibility of a current infection. Some people may take longer to make antibodies, so a negative result may be due to inaccurate timing of the test.


Studies in people with novel coronavirus infection suggest that the presence of antibodies in the blood may reduce the likelihood of reinfection with the virus. However, recent studies suggest that this may not be permanent. A Public Health England (PHE) 2021 study, currently in preprint*, suggests that seroconversion of COVID-19 antibodies may provide 83% protection for at least five months.


Nonetheless, antibody testing may be important for identifying segments of the population that have been exposed to coronavirus and have developed herd immunity, at least in the short term.    


Antibody testing may also be used to identify individuals who have recently recovered from coronavirus infection and are eligible to donate blood for recovery plasma therapy. However, recent studies have questioned the effectiveness of plasma donation for COVID-19.