Nucleic acid Test, Antigen Test, and Antibody Test For COVID-19

There are three main methods of COVID-19 detection, namely nucleic acid test and antibody test, and antibody test. Their detection principles and detection purposes are different.

Nucleic acid test

Nucleic acid test – diagnose (or rule out) active coronavirus infection

Such tests include PCR and NAAT, which detect the presence of viral genetic material (RNA) using nasopharyngeal, nasal, or throat tests or saliva samples. Nucleic acid test results are generally regarded as the “gold standard” and do not need to be repeated to verify.

Viral RNA is present before antibodies are formed or symptoms appear, allowing early detection of infection. PCR-polymerase chain reaction is the most commonly used nucleic acid test.

During the test, a substance called reverse transcriptase, or DNA polymerase, is added to a nasopharyngeal sample. If it encounters a virus, this substance copies the viral RNA in large numbers, producing billions of copies, enough to cause a positive result.

This is because the primers and probe antennae in the reagent attach to the sequence of the virus’s genetic code, signaling the discovery of the pathogen.

PCR tests need to be sent to a laboratory for analysis, usually with results within 24 to 48 hours; If used to identify specific variants, it may take longer.

Antigen Test

Antigen testing — rapid diagnosis (or exclusion) of active coronavirus infection

Also known as rapid detection, antigen rapid detection, rapid self-testing and other different terms, using nasopharynx, nose or throat test or saliva sample, check the surface of the virus protein. Positive test results are more accurate, but negative results may include “false negative”, that is, when the test has been infected with the virus but has not formed antibodies, so negative.

If the antigen test is positive, a nucleic acid test is usually performed to determine infection.

The ADVICE from the NHS is that if you have a positive LFT test, you should get a POLYMERase chain reaction (PCR) test, which is a nucleic acid test, to confirm if you have COVID-19.

The two main features of antigen testing can be read from its name: one is fast – results can be obtained in 15-30 minutes; The second is self-testing — sampling and testing by themselves, without sending to the laboratory.

Antibody Test

Antibody testing — to find out if you’ve ever had coronavirus

Also known as a serum test, a blood sample is used to see if antibodies against the virus have been developed. People who have recovered from viral diseases have varying levels of immunity. Like antigen tests, antibody tests can yield false negative results early in the infection.