For diseases caused by viral infections, in order to clarify the types of viruses to be treated, the following two types of inspections can be performed:
1. Direct detection of the virus itself
2. It can detect the antigen on the surface of the virus and the nucleic acid of the virus.
The test identified the antibodies produced in order to resist the virus:
Under normal circumstances, antigen testing does not require high laboratory conditions, and is mainly suitable for large-scale screening in primary hospitals; antibody testing is easy to operate, and the test results can be obtained in 10-15 minutes. Nucleic acid detection requires many laboratory conditions, intermittent personnel, and equipment, but the result page is the most sensitive and accurate.
Of the 10 new coronavirus nucleic acid detection reagents that have been approved, 8 of them all use the fluorescent PCR method, and the remaining detection methods are the combined probe-anchored polymerization sequencing method and the constant temperature amplification chip method.
1. Fluorescence PCR method
The PCR method refers to the polymerase chain reaction, which can greatly increase the trace amount of DNA. When used to detect the new coronavirus, because the new coronavirus is an RNA virus, it is necessary to reverse transcribe the viral RNA into DNA before performing PCR detection.
The principle of fluorescent PCR detection is that as the PCR proceeds, the reaction products continue to accumulate, and the fluorescence signal intensity also increases in proportion. Finally, the change in the amount of the product is monitored by the change in the fluorescence intensity, thereby obtaining a fluorescence amplification curve.
This is currently the most commonly used method for nucleic acid detection of the new coronavirus. However, the following factors may cause errors in the test results:
Improper storage or failure to submit for testing: RNA viruses are easily degraded. Therefore, after obtaining patient samples, they need to be stored in a standardized manner and tested as soon as possible. Otherwise, the test result is likely to be inaccurate.
Error interpretation of results: The currently approved test products are selected based on the open reading frame 1a/b, envelope protein and nucleocapsid protein of the novel coronavirus genome. However, the detection primers and probe designs of different products are different, and there are differences in the detection and interpretation of single-target segments, dual-target segments, and three-target segments. Therefore, if the interpretation is not strictly carried out in accordance with the different instructions, it may lead to wrong judgment of the result.
2. Combined probe-anchored polymerization sequencing method
This detection is mainly to use a special instrument to detect the gene sequence carried by the DNA nanospheres on the sequencing slide.
This kind of detection has high sensitivity and is not easy to miss the diagnosis, but the results are also easily affected by many factors, including:
Samples not tested in time: Like the fluorescent PCR method, the results may be inaccurate if they are not stored in a standardized manner and tested as soon as possible.
The room temperature of the test site is too high: This will also affect the accuracy of the test results. Different testing instruments and kits may also affect the results.
3. Constant temperature amplification chip method
Gene chip detection is one of the traditional virological diagnostic methods. The detection principle is a detection method developed based on the complementary binding characteristics of nucleic acids, which can be used to qualitatively or quantitatively measure nucleic acids present in organisms. Compared with PCR, gene chip has higher accuracy rate and shorter time, but it is also more expensive and the detection throughput (the amount of data that can be generated per unit time) is relatively lower.
The thermostat chip approved this time can detect six types of respiratory viruses, including the new coronavirus. Results can be obtained within 1.5 hours,
Compared with PCR, gene chip has higher accuracy rate and shorter time, but the price is more expensive, and the detection throughput (the amount of data that can be generated per unit time) is relatively lower.
4. Virus antibody detection
Antibody detection reagents are used to detect IgM or IgG antibodies produced by the human body after the virus enters the human body. IgM antibodies appear earlier and IgG antibodies appear later.
At present, the five new coronavirus antibody detection reagents that have been approved use the colloidal gold method and the magnetic particle chemiluminescence method.
5. Colloidal gold method
The colloidal gold method uses colloidal gold test paper for testing, which is the quick test paper often referred to at present.
This kind of test paper is specially marked and has holes on it, which is used to drip the serum sample of the examinee. There are two lines on the colloidal gold test paper, one is called the test line and the other is called the quality control line. If both lines are colored, it means positive; only the quality control line is colored, which means negative; except for these two cases, it belongs to Invalid result.
