1 What is Coronavirus Antigen test？
Coronavirus Antigen test detects the virus itself by the specific proteins (i.e. Antigens) on its surface, so as to identify the existence of the virus.
2 What is the difference between Coronavirus Antigen test and Antibody test?
Antibody test is to detect the molecules (i.e. antibodies) that people produce after being infected with the virus. Antibody may take several days to produce after infection, and usually remain in the blood for several weeks after the patient recovers. That is, the cured patient can also be tested positive for a longer period of time. Therefore, the antibody test has very limited use in the diagnosis of COVID-19.
The Antigen test is to detect the virus, which directly relates to the infection itself.
3 What is the difference between Antigen test and nucleic acid test?
Antigen test is based on immune reaction, while nucleic acid test is based on genetic information. Therefore, Antigen test can be much faster than nucleic acid test (PCR) (15 minutes vs 4 hours). Certainly, the cost of speed is the sensitivity. That is, Antigen test is not as sensitive as nucleic acid test. PCR can detect micro amount of SARS-CoV-2 virus due to the amplification process of virus genetic information. This is also why PCR test often takes several hours and may cause aerosol contamination.
4 Advantages of Antigen test and precautions in application
Except for advantages of rapid test, it does not require laboratory processing and medical professionals to operate. Therefore, it is very suitable for large-scale general screening when lacking laboratory conditions and medical professionals. However, if human body contains a very low amount of virus, and with no obvious clinical symptoms, they are likely to be tested negative. The ability of such infected people to spread the virus is also much lower than that of ordinary patients. Therefore, for asymptomatic infected people, it is recommended to adopt nucleic acid for detection.
Antigen test helps to quickly identify people with high levels of infection (those who are most likely to infect others). Therefore, Antigen test can help prevent the spread of the pandemic, by identifying those who are most likely to spread the disease and isolating them from others. Thus, shift the focus to identify the most infectious people.
5 Precautions for Antigen test operations
Antigen test is to detect the virus itself, so sample selection is very important. We recommend sputum sample, since sputum is the secretion from respiratory tract where viruses cluster the most, so sputum is relatively easy for detection.
Because of the uneven distribution of the virus on the nasopharyngeal mucosa appearance, it is very likely that no virus or very small amount of virus is taken while sampling and lead to false negative result, when sampling via throat swab. Therefore, the accuracy will be lower than that of sputum.
In addition, studies have shown that after people are infected, the viruses can be detected in the digestive tract, especially in the intestinal stool. Therefore, if convenient (e.g. in hospital or at home), stool sample is another option for testing; Saliva samples mixed with sputum also have a certain probability of detection, although the amount of virus contained is lower than pure sputum.
For false negative testing result (PCR positive, Antigen test negative), if the patient has asymptomatic infection, it is recommended to take nucleic acid as standard, and if patients cough or have other symptoms, it’s suggested to re-sampling and test again. Besides, S protein is selected as the testing object in the New Gene’s Antigen test. S protein shows good specificity and usually does not cause false positive results.
The WHO has always been a supporter of Antigen testing. Experts pointed out that compared with conducting an accurate test every two weeks, conducting a relatively insensitive quick test twice a week can more effectively contain the spread of SARS-CoV-2. That is, the focus of the virus detection should be on identifying those who are likely to spread SARS-CoV-2, rather than locating anyone who is infected with SARS-CoV-2.
Delhi is the first place in India to start using rapid Antigen testing in June. By mid-July, the number of cases there had been reduced, and the daily death toll had also stabilized, indicating that Antigen testing played a certain role in controlling the spread of the virus. Although after cases declined, India began to lift the blockade restrictions and cause the infection to rise again.
The Philippine Association of Microbiology and Infectious Diseases has issued interim guidelines for clinicians and medical staff, stating that Antigen testing can be used as a substitute for PCR to diagnose coronavirus infection in people with symptoms in the early stage, especially during the acute infection period