The principle of nucleic acid and antibody detection of new coronavirus

The new crown is an acute respiratory infectious RNA virus. It is spherical in shape, with crowned spikes on the surface, ribonucleic acid strands (RNA) inside, and shells composed of multiple proteins on the outside.

Early diagnosis of infected persons is an important prerequisite for controlling the spread of the epidemic and for active treatment. At present, two technologies are mainly used to diagnose whether they are infected by the new coronavirus, one is nucleic acid detection technology, and the other is antibody detection technology.

Nucleic acid testing is a direct detection of viruses, requiring respiratory samples, including pharynx, nasopharynx secretions, sputum, bronchus, lavage fluid, lung biopsy, etc. The collection process is very complicated. The storage conditions of nucleic acid samples are harsh, RNA is easy to lyse, and can only be stored for 24 hours at 4°C. It uses the unique gene sequence of the virus as the detection target. Through PCR amplification, the target DNA sequence we choose increases exponentially. Each amplified DNA sequence can be combined with a pre-added fluorescent labeled probe. Combined to produce a fluorescent signal. The more target genes that are amplified, the stronger the accumulated fluorescent signal. In samples without virus, since there is no target gene amplification, no increase in fluorescence signal can be detected.

The antibody test is an indirect test, which can also be said to be a blood test. It can be collected by peripheral blood or venous blood. The sample collection method is more convenient and safer, and the sample can be stored for 72 hours. It is not against the virus itself, but the specific antibody produced by the immune response after the human body is infected with the virus. The human body gradually produces antibodies about a week after being infected with the virus and then rapidly rises. Generally, the human body first produces an antibody called IgM, which does not last long; then a large number of IgG antibodies appear, which may last for several months. several years.

IgM and IgG antibodies can be used for the auxiliary diagnosis of the new coronavirus, which is complementary to nucleic acid detection, reduces the missed detection of patients, and can assist in monitoring the progress of the patient's disease. It should be noted that in the early stage of the disease, it may not be detected due to less antibody production, which is the "window period." However, due to differences in pathogenicity and immune function of the organism, there are individual differences in the appearance time and expression level of specific antibodies in different patients.

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