Is nucleic acid testing as we know it?

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What is nucleic acid testing?

"Doctor, I want to do nucleic acid!"

"May I ask which project are you doing nucleic acid testing?"

"Ah? Is there any other nucleic acid test?"

At present, when the public mentions nucleic acid testing, they automatically think that "nucleic acid testing = new crown testing". In fact, the nucleic acid test of the new crown is only one of the nucleic acid tests. Nucleic acid detection methods are widely used in the detection of pathogenic microorganisms as an important means of diagnosing diseases and monitoring viral load, such as the well-known quantitative detection of hepatitis B virus DNA, human papillomavirus (HPV) detection, human immunodeficiency virus (HIV) RNA detection, etc. Therefore, in terms of detection scope, "nucleic acid detection > new crown detection".

So, what is nucleic acid?

Pick your mouth? Poke the nose? Why not take blood?

At present, the routine sample collection methods for respiratory virus nucleic acid detection include: throat swab and nasopharyngeal swab. Also known as "poke the nose" and "poke the throat".

"Doctor, which one is more comfortable then?"

"Well...this varies from person to person. The sensitivity of different parts of each person is different, but they are not very comfortable. For testing, the accuracy of nasopharyngeal swabs is higher."

"Doctor, can this nucleic acid test take blood?"

"can not……"

Because, after the respiratory virus infects the human body, it will first "root" and multiply in the respiratory epithelial cells. Therefore, upper respiratory tract specimens (nasopharyngeal swabs, throat swabs, sputum, and bronchoalveolar lavage fluid) have the highest positive rates. Since the virus may not have invaded the patient's blood in the early stage of infection, the viral nucleic acid in the blood is likely to be negative at this time, and such a false negative result will lead to missed detection.

How does nucleic acid testing "catch" the virus?

Step 1: Storage and Shipping

After sampling, the swab is placed in the virus preservation solution. The virus preservation solution can maintain the activity and integrity of the virus. At the same time, the preservation solution contains a variety of antibiotics, which can inhibit the growth of other bacteria and fungi in the sample, and defeat the "competitive partner". The virus can monopolize the "comfortable" environment and live "freely" in this paradise. .

Step 2: Shake

After the virus sampling tube is sent to the testing laboratory, it is fully shaken, and the respiratory epithelial cells and virus adhering to the swab can not be "shaken" into the preservation solution.

Step 3: Extract Nucleic Acids

(1) Cracking

Denature the protein coat with guanidine salts. Only by pulling out this colorful protein "vest" can the nucleic acid of the virus be released, revealing the "true face" of the virus.

(2) Combine

Add magnetic beads to bind to nucleic acids. Say "goodbye" to all kinds of cell debris, proteins...!

"our target is?"

"Grab the nucleic acid!"

(3) Washing

Can you catch nucleic acid with one combination? How can it be so easy! It was caught, but there were still a small amount of debris, and the protein was still stuck together with the nucleic acid. How to improve the purity of nucleic acid? We have two magic weapons: add salt and add acid.

"Adsorbed Nucleic Acids - High Salt Low pH"

"Elute Nucleic Acids - Low Salt High pH"

Repeat the adsorption and elution two or three times to realize the extraction and purification of nucleic acid. The rest is "naked" nucleic acid.

Step 4: Detection of Nucleic Acids

The routine screening of respiratory virus nucleic acid detection adopts real-time fluorescent PCR method.