Recently, the frequency of epidemics across the country has increased significantly, with more than 550,000 cases of indigenous infections reported since April. Round after round of nucleic acid has become a daily routine for many people.
In Shanghai, Jilin and other places, antigen detection is widely used as an important supplement to nucleic acid detection.
At the same time, is it true that a message that "cola, orange juice, vinegar, and kimchi will make antigen tests falsely positive" circulated online?
Some people also directly dripped different drinks on the kit, and the result was that Coke was weakly positive.
Will beverages really cause a "false positive" for COVID-19 tests? Life Times (search for "LT0385" in WeChat to pay attention) interviews pathogen biology experts on this issue, interprets the factors affecting the test results, and reminds you of the precautions for the nucleic acid testing process.
Experts interviewed
Jieliang Chen, Associate Professor of Pathogenic Biology, School of Basic Medical Sciences, Fudan University
This article is written by | Life Times reporter Tian Yuting
This article was edited | Wang Bingjie
Why do "false positives" occur?
Chen Jieliang, associate professor of pathogenic biology at Fudan University's Basic Medical College, said that the possibility of drinking a drink makes the new crown test result "yang" is very low, and there are three main cases that can make the "antigen test" false positive.
1
Antigen detection has a fault tolerance rate
The national "Quality Evaluation Requirements for Novel Coronavirus Antigen Detection Kits" stipulates that under the premise of sampling in strict accordance with the specifications of the instructions, the test results of the kit are allowed to have a certain probability of false positive or false negative.
For example, the specificity of a certain kit is 98.8%, and the false positive rate should be 1.2%, but the actual proportion in some high-prevalence areas can be only 1 in 10,000. That is to say, antigen detection is indeed possible to be "false yang" and "false yin", but the probability is extremely low.
2
Buffers are not used correctly
A study published in the International Journal of Infectious Diseases did find that sweet drinks, energy drinks, alcoholic beverages, etc. can all cause "false positives" in antigen tests, which is actually related to the pH of beverages. This is completely avoidable if mixed with an equal amount of buffer and then retested.
The antigen self-test kit uses the "colloidal gold immunochromatography method", that is, the protein (antigen) on the surface of the new coronavirus is combined with the colloidal gold labeled antibody to aggregate in the C region, showing "two bars".
Since the binding process is affected by pH, the sample must be "passed through" buffer. Therefore, the standard procedure for antigen detection is to sample the sample mixed in an extraction tube containing buffer and dripped into the sample well.
The experiments on the Internet are all directly dripping beverages, vinegar, soy sauce and other substances into the detection card, skipping the buffer ring, completely beyond the scope of the kit. Fundamentally, this is an irregular operation and is not a so-called "false positive". If you don't trust the results of an antigen test, you may want to test again or change the brand test.
3
The specimen is contaminated
If antigen testing is to check the "clothes" of the virus, then the nucleic acid test is aimed at the "bones" - internal genetic material. Nucleic acid test results are the most accurate and remain the gold standard for COVID-19 pathogen testing. The "false positive" of nucleic acids is mostly caused by laboratory contamination or improper handling, and is not related to diet.
Since nucleic acid testing is more accurate, why should antigen testing be used in some places?
Although the sensitivity is not as good as nucleic acid detection, the advantage of antigen detection is "fast", suitable for large-scale screening, home isolation population, and grass-roots hospital applications without nucleic acid detection capabilities, which can help nucleic acid detection "fight the front battle" and greatly reduce the detection pressure.
If the antigen test is "yang", and then through the nucleic acid test review, both show "yang" is confirmed, and the nucleic acid "yin" can be considered as false positive.
Live-action demo: How nucleic acid testing can avoid cross-infection
What do individuals need to pay attention to when queuing up in a concentrated line to do nucleic acids? How to protect against cross-infection? Combined with Chen Jieliang's reminder, Life Jun used a video to demonstrate for everyone.
Before nucleic acid testing
Although diet does not affect the positive result, in order to avoid false negatives, it is recommended not to eat, drink, smoke, drink, or eat gum within half an hour before sampling, so as not to dilute oral secretions.
Not eating before sampling can also prevent nausea and vomiting during nucleic acid sampling.
Nucleic acid testing
Consciously and orderly queuing during testing, batch and time-sharing detection. Avoid gathering in elevators and corridors. People who have glasses in this process can wear glasses.
Always keep a distance of 1 to 2 meters (at least 1 meter) during the queue, try to avoid talking, making phone calls, and wait quietly and patiently.
Do not touch the collection workbench with your hands, mobile phones, and ID cards.
When removing the mask, do not pull the mask to the chin, gently pinch the lanyard on both sides, and remove the mask to avoid touching the surface of the mask.
Hold your breath when taking off the mask for sampling, avoid inhaling aerosols, and quickly put on the mask after sampling.
If there is discomfort in the pharynx and nose, do not sneeze at people around you, the correct way is not to take off the mask and cover it with your own elbows; let alone spit freely.
If you bring a child when doing nucleic acid, parents should take good care of it to avoid children from touching and running around.
After nucleic acid testing
Leave as soon as possible after the sampling is complete, and do not talk or linger at the sampling point.
Hang your coat to a ventilated place when you get home and wash your hands in a timely manner.
Personal belongings such as mobile phones and ID cards can be disinfected with alcohol pads.
The consequences of falsifying test results are serious
Originally, the antigen test that ignored the operating specifications yielded a "positive" result that did not make sense.
But a Tik Tok netizen named @missleanne1 shared the method on the Internet through video in June 2021, prompting many students to follow suit and use this as an excuse to skip class.
Is there a way to determine whether the test results are fake? The teacher quickly figured out the identification method: wash the false positive kit with buffer, and the test result will return negative.
COVID-19 kits that present fake positive results
On top is a cola-infused kit, and on the bottom is the same brand kit that has been rinsed with buffer
Skipping class with false positive results in foreign countries will only cause teachers a headache, and falsifying test results in China is not conducive to checking the risk points of the spread of the new crown virus and curbing the spread of the epidemic.
Whether it is antigen testing with cola, orange juice, or water, or "falsifying" when reporting antigen test results is not advisable. The public security departments have made it clear that for nucleic acid testing that should be inspected, the epidemic prevention regulations are violated, and the epidemic prevention order is deliberately disrupted, the principle of combining education and punishment will be upheld, and the public security organs will punish those who refuse to make corrections and the circumstances are serious according to law. ▲
Editor: Zhang Jie Video Producer: Yang Meng Zhao Ziying