Differences between Covid-19 Nucleic acid test, antigen test and antibody test

There are usually two strategies for detecting infectious diseases: testing for the pathogen itself, or testing for antibodies produced by the body to fight it off.

Among them, detection of pathogens can detect both antigen and nucleic acid.

Nucleic acid testing and antibody/antigen testing are important means of confirming the Novel Coronavirus as well as an important procedure for the diagnosis of patients.

I. Detection method of rapid antibody test and antigen test kit

(1) Nucleic acid testing

Nucleic acid detection, as a direct method to detect the genetic material of pathogens, has been widely used in this epidemic because of its characteristics of early diagnosis, high sensitivity and specificity. It uses gene sequencing technology to obtain nucleic acid sequence for diagnosis, but the accuracy of this detection method largely depends on the sampling location and technique, so improper sampling may lead to inaccurate results.

(2) Antigen detection

Antigen detection is the detection of pathogenic bacteria antigen, is also a direct detection of pathogenic bacteria method. As an antigen component, pathogenic protein can induce immune response and produce immune effector substances (such as antibodies). When the novel Coronavirus invades the human body, proteins such as the S protein (spike glycoprotein) on its surface are antigens. The key of antigen detection products is to develop antibodies that can specifically bind to antigens, which is also the technical difficulty of developing antigen detection products.

(3) Antibody detection

Different from pathogen nucleic acid detection and antigen detection, antibody detection is the host immune response, which is an indirect detection method, mainly used for infection tracing investigation. After the virus invades the human body, the human body produces corresponding specific antibodies for defense, among which specific antibody IgM is the first to produce and carry out early defense, followed by IgG antibody. By detecting the presence and content of specific antibodies IgM and IgG in blood samples, we can indirectly judge whether there is virus in the body and the situation of virus infection.

II. The characteristics of three detection methods

Nucleic acid testing: it has high requirements for laboratory environment, testing personnel, instruments, etc., with high sensitivity and good specificity. Results are generally obtained within 2-3 hours.

Antibody detection: easy to operate, suitable for the detection of a large number of suspected cases and asymptomatic infected persons, the fastest results within 15 minutes.

Antigen detection: low requirements for laboratory, can be used for early screening, early diagnosis, suitable for large-scale screening in basic hospitals, the fastest results within 15 minutes.