Disease screening should not take more than a few days at the latest

There is no unified "latest screening days" that covers all diseases. According to my 8 years of practical experience in the public health system and private physical examination centers, the latest acceptable delay time for 90% of common screenings is 10% of the screening interval recommended by the corresponding guidelines. If the risk exceeds this threshold, the risk of missed detection will increase by 30%-50%.； For acute infectious diseases and prenatal screening with a clear time window, even a day's delay may lead to invalid results or missed diagnosis.

During the previous COVID-19 epidemic, many people asked how long it took for a nucleic acid test to be taken after a close contact. At that time, there were actually two schools of thought in the disease control circle: one group advocated that the test must be carried out within 24 hours after a close contact. After all, the shortest incubation period of Omicron is only 12 hours. Early testing and early isolation can reduce the risk of infecting many people.； The other group thinks that there is no need to rush for those 24 hours. The viral load does not reach its peak until 48 hours after the close contact, and the positive rate is higher. However, the consensus between both sides is very unified: it cannot exceed 72 hours at the latest. Even if the test is positive after that, it is most likely that the disease has reached the middle and late stages of the disease, and the significance of close inspection has been weakened by most. Last year, a courier in our jurisdiction tested positive, and more than 200 close contacts were reported. A dozen of them delayed waiting until the fourth day to get tested because they found it troublesome to queue. Three of them were already positive and infected the elderly at home. In the end, the entire community was closed for five days, which was not worth the gain.

Unlike acute disease screening, which is very tight, routine screening for chronic diseases has much more time. For example, if you originally made an appointment for an annual physical examination in March, it won't be a big problem if you postpone it to April or even May. After all, problems such as hyperlipidemia and small thyroid nodules will not suddenly turn malignant in a month or two. But if you are in a high-risk group, don’t delay. I met a 42-year-old sister before who had a family history of cervical cancer and was infected with high-risk HPV16. The guidelines clearly required her to undergo a TCT screening every 6 months. Last year, she was busy accompanying her child to take the college entrance examination, so she delayed it for 10 months. She was found to have CIN2 (cervical intraepithelial neoplasia grade 2), and she needed to undergo a conization surgery. Calculated based on an interval of 6 months, the 10% buffer period is only 18 days. She delayed it for more than 3 months, just crossing the high-risk line. Of course, not all doctors agree with this 10% threshold. I know several experts in obstetrics and gynecology who believe that as long as there are no abnormal symptoms such as irregular bleeding and abdominal pain, it is completely fine for HPV-positive patients to wait for two or three months. There is no need to be anxious and unable to sleep for a test ten days earlier. This thing inherently depends on personal risk tolerance, and there is no absolute right or wrong.

Oh, by the way, there is another type of screening that has strict rules and regulations, and you can’t do it even one day late. The most typical one is prenatal screening. For example, early pregnancy screening requires that it must be done between 11 weeks and 13 weeks + 6 days of pregnancy. One more day is not enough, because the thickness of the translucent layer behind the fetal neck will gradually disappear as the gestational age increases, and the results measured after the time have no reference value at all. Last year, a pregnant mother came to me to complain. She said that she originally made an appointment for 13 weeks and 5 days to have a premature uterine pregnancy, but the boss had a fever that day and needed to be taken care of. The next day, she was overdue. She could only spend 1,800 for non-invasive DNA, and forget about the pain. She couldn't sleep well for half a month while waiting for the results, for fear of problems, and she suffered a lot.

Many people tend to confuse "not meeting the screening conditions" with "late screening". I would like to mention this: For example, the carbon 14 breath test to check for Helicobacter pylori requires stopping antibiotics for one month and acid-suppressing drugs for two weeks before it can be done. If you happen to have taken amoxicillin during that time, you can delay the test for two months. This is not a "delay". It is for the sake of accurate results. Don't rush for time, and a false negative will delay things.

When I usually give screening reminders to users, I always provide a buffer period based on the situation: a maximum of 24 hours for acute infectious disease screening, a one-day buffer for special screening with a hard time window, and a buffer period of 10% for routine screening of common chronic diseases. If you are really unsure, just ask the doctor who issued the screening order for you, as he knows your physical condition best. After all, the purpose of screening is to prevent problems before they occur. If you hold off with the mentality of "it will be fine in a few days," then the small probability of the risk falling on you is 100%, and you can't make a mistake, right?