The sudden outbreak of the COVID-19 virus causes chaos in the whole world. It is a severe respiratory disease and is easily transmissible, thus posing a severe threat to our health. When the outbreak of a highly transmissible disease starts, the first line of action should be early testing and diagnosis of the virulent.
Early testing leads to rapid identification of infected persons, or quick treatment, and taking all the necessary preventive measures to prevent the spread of the diseases.
COVID-19 tests can detect either the SARS-CoV-2 virus or the antibodies that our body produces after getting an infection or antibodies that develop after vaccination. Main molecular tests that can identify infection caused by the COVID-19 virus (SARS-CoV-2) are:
- Molecular test: RT-PCR test, NAAT (nucleic acid amplification test)
- Antigen test
- Antibodies test
All tests are different as each detects a distinct part of the virus. Test speed and its accuracy are also different in these tests.
Before discussing the test procedures separately, let’s understand antigen and antibodies. Antigens are the proteins present on the outer shell of the virus. Antibodies are produced in our body against specific antigens to protect our body from infection.
For conducting any test that detects COVID-19 infection, the first step is to collect the sample from the suspected person. A health care worker takes a sample of secretion from the nostrils and the nasopharynx using a long swab with a soft end. This sample contains both the person’s and the virus’s RNAs.
The reverse transcription-polymerase chain reaction test is also known as the RT-PCR test. It is a gold-standard test for diagnosing viral diseases like Ebola and SARS-CoV-2 virus infection.
The RT-PCR is a sensitive test. It means that if someone has COVID 19 infection, higher are the chances of this test giving a positive result. It can also detect residual viruses even after the person has recovered fully.
After collecting a sample from a person, the pathologist extracts the RNAs (host and virus both) from the sample secretion. The genetic material (RNAs) of the virus is created with the help of a reverse transcriptase enzyme and amplification in the laboratory. After recovering genetic material, a fluorescent dye is used that identifies if the virus is present or not. The entire process of fluorescent dye takes up to 8 hours to detect whether the sample is positive or negative.
Rapid antigen test
Rapid antigen tests detect the protein present at the outer surface of the Coronavirus. The total time taken by test to provide results is 15-30 minutes. Antigen test is a point-of-care test. It means it can be done anywhere, like at the clinic, home, or hospital.
Antigen tests are relatively less expensive. Although it is less sensitive than the RT-PCR test, the antigen test is an effective way to monitor infection in people who are in close contact with COVID-19 infected.
Rapid antigen tests are often used as mass screening tests to detect SARS-CoV-2 infection quickly in containment zones or healthcare settings. It helps in the immediate implementation of infection prevention measures effectively.
A rapid antigen test is a simple test. It comes as a kit same as a pregnancy test kit. Before taking the sample, wash your hand for 20 seconds using soap and water. Alternatively, you can use hand sanitizer. After taking the sample swab from the nose and throat, we can transfer it to the extraction tube and finally to the test strip.
You can expect a result in 15 minutes. But in the case of a false-negative test result, that is, the patient is asymptomatic but has an infection, the rapid antigen test is not reliable. In that case, the RT-PCR test is the test of choice for confirmation.
Always remember, while you are waiting for the test results, you should quarantine yourself. If you are not sure about COVID-19 infection in you, please take guidance from your healthcare provider and immediately go for the test suggested by your doctor.
Dr. Srinath Kumar T S | Senior Consultant and HOD – Emergency Medicine | Mazumdar Shaw Medical Center, Bommasandra, Bangalore