With the resolute implementation of the policy of zero air defense dynamics during the epidemic, nucleic acid testing is becoming increasingly frequent in various regions of the country. It is a familiar expectation for everyone to repeatedly test negative results. However, as a result of nucleic acid testing, there is not yet much accurate public understanding of the Ct value. What factors actually affect the Ct value?

What is the significance of adjusting the Ct value from 40 to 35

Firstly, let's start with the Ct value. COVID-19 is very small. To detect it, it is necessary to replicate specific genes for many times, so as to magnify it for observation. Each amplification of the virus results in a Ct value of 1 unit, which is a power multiple of 2. For example, if you magnify 2 to the 35th power, the Ct value is 35.

The Notice on Printing and Distributing the Diagnosis and Treatment Plan for novel coronavirus Pneumonia (Tentative Ninth Edition) issued by the National Health Commission has adjusted the criteria for nucleic acid detection when removing isolation or discharging from hospital, reducing the Ct value of nucleic acid detection from 40 to 35, which is in line with international standards. In other words, in the future, when the Ct value is greater than 35, it will no longer be counted as a positive nucleic acid test. To put it more simply, if the number of viruses is reduced, the infectivity and transmission power will be reduced. The Ct value amplification factor is adjusted from 40 to 35, which means that viruses that can only be detected at a magnification factor of 35 or above will not be detected after adjustment.

Zhang Wenhong once said in a media interview that when the epidemic first arrived, based on the overall requirements of epidemic prevention, the Ct value was ultimately set at 40. At the same time, relevant departments and experts were also studying while fighting against the epidemic. Through research, it has been found that when the Ct threshold is set to 30 times amplification, the basic infectivity is already very low; Continuing to raise to 35 has been widely recognized.

Zhang Wenhong pointed out that this threshold reduction is a significant adjustment, which means that as long as the value reaches 35, the patient's hospitalization time will be greatly reduced. In the future, they only need to stay in the hospital for 7 or 10 days. Staying in the hospital for a long time is meaningless for treatment, and it is extremely unreasonable to stay in the hospital if it is not infectious. For example, in Shanghai, the average hospital stay of COVID-19 patients is 15 days now, which may be reduced to 10 days after nucleic acid adjustment, so that infected people can return to normal life as soon as possible, and also avoid waste or even run on medical resources.

Another key point is that when the Ct value reaches 35, the relevant personnel no longer need to be quarantined in the quarantine hotel for 2 weeks, but can adopt a home observation method. Zhang Wenhong stated that making such a significant decision is not easy, as it is based on the accumulation of numerous scientific studies, as well as the foundation of evidence-based medicine and scientific research.

Zhang Wenhong gave the following evaluation on the adjustment of Ct value: this is a very important step we have taken in the field of intelligent epidemic prevention. I hope that in the future, the fight against the epidemic will be achieved step by step, in order to achieve the goals expected by the country and the people.

So besides the amplification factor directly affecting the Ct value, are there any other reasons that can affect the Ct value? What is the Ct value of the healthy population after the positive diagnosis of COVID-19?

According to public media reports, a research team found that after recovery, the human body still intermittently expels respiratory mucosal cells in weeks or even months. These cells contain fragments of COVID-19 disease virus RNA, which are sometimes detected by RT-PCR, resulting in "repeated and erratic" results. If the CT value of such "re positive" patients is high, coupled with the inability of the sample to culture the virus and the presence of antibodies in the body, then the detected sample is a dead virus fragment and has no infectivity. The research team studied dozens of locally suspected second degree infected patients and found that the circulating threshold (Ct value) of all re positive tests was higher than 30 or even 35, indicating that they had no live viruses in their bodies.

Will immunity affect nucleic acid test results

The indicator of nucleic acid testing is the Ct value. Obviously, how to make the nucleic acid test result negative, ensure that the Health Code does not pop up, and maintain a green code is a topic of concern for every citizen. Is there any medicine that can kill COVID-19?

Professor Zhang Wenhong, Director of the Department of Infectious Diseases at Huashan Hospital affiliated with Fudan University, has already given the answer. He once said, "The most effective drug is the human immune system." The immune system is also known as the "best doctor in the world" and can defeat bacteria and viruses that invade the human body.

The same is true for those who have been exposed to COVID-19 patients. Some people are infected, but some people are not; It is also infected with COVID-19. Some people will get better in a few days, while others are getting worse and worse, and even need to be treated for a long time, even life is in danger. In fact, these are all closely related to the body's immune system.

Although there is no scientific experiment to prove how much COVID-19 can be killed by immunity. However, more and more experts in traditional Chinese medicine and western medicine can reach a consensus that people with strong immunity can quickly kill the COVID-19 virus that invades the human body, while people with weak immunity, where COVID-19 has the upper hand, will proliferate in large numbers in the body, resulting in COVID-19 symptoms in the human body.

According to this line of reasoning, if someone is unlucky to be infected with COVID-19, even if only a part of the virus is killed due to strong self immunity, as long as the Ct value is less than 35 during nucleic acid testing, the result may also be negative. If a patient diagnosed with COVID-19 can quickly kill a part of COVID-19 by his own immunity, the probability of a negative nucleic acid test Ct value less than 35 will be greatly increased. On the contrary, patients who have recovered from COVID-19 infection, even if they carry dead virus fragments, may also have positive nucleic acid test results if their immunity is low. It is gratifying to note that the confirmation of COVID-19 infection is not based on the single nucleic acid test results as the only criteria. However, due to a low immune system, a positive nucleic acid test can bring unnecessary troubles such as re examination, isolation, and psychological pressure.

Several signals of low immunity must be taken seriously

Since immunity can affect the results of nucleic acid testing, what kind of situation is a manifestation of low immunity? How can the general population have a clear understanding? The author has consulted relevant materials and found that they can make rough judgments based on common situations in daily life.

It is particularly prone to catching a cold, with small wounds that cannot heal for a long time, repeated blistering on the lips, sudden worsening of athlete's foot in people with athlete's foot, discomfort in the stomach, diarrhea, and vomiting. Any of these situations should be vigilant.

In addition, the most easily overlooked manifestation of low immunity by the public is fatigue and a feeling of lack of energy. Many people may think that they haven't rested well, but in reality, it is often a problem caused by a weakened immune system. When the human immune system is weakened, bacteria and viruses are prone to invading the body, and the immune system cannot immediately eliminate these invaders, which can easily lead to a prolonged battle and increase the body's consumption, making people feel very fatigued.

Not only for the sake of our own physical health, but also to increase the probability of negative nucleic acid test results, improve immunity, and fight the epidemic for all, let's start from each of us. (Text/Binghan)