Disease screening and census belong to several levels of prevention

In most cases, disease screening and general examinations belong to secondary prevention. A small number of pre-screenings for specific causes and complications screening for patients with chronic diseases may be classified into primary prevention and tertiary prevention respectively, which is not an absolute one-size-fits-all classification.

To clarify the origin of this classification, we must first talk about the three-level prevention framework that has been used in the field of public health for almost a hundred years. The core of the secondary prevention we often talk about is the three early principles of "early detection, early diagnosis, and early treatment". It specifically targets those diseases that have quietly occurred but have not yet shown obvious symptoms, and nip the signs in the bud. Last year, I helped the community health service center near my home sort out the two-cancer screening ledger. Among the more than 3,000 middle-aged women who participated in the examination, 12 cervical cancers in situ and 8 early-stage breast cancers were found. These people had not felt any discomfort before. If they had to wait until they felt lumps or bleeding before going for the examination, they would most likely have reached the mid-to-late stage. Not only would they have to undergo breast surgery, radiotherapy and chemotherapy, but their survival rate would also be halved. This kind of general screening, which targets healthy people and screens for early-stage diseases in the asymptomatic stage, completely relies on the core definition of secondary prevention. It is also the type of screening we see most often.

But don’t think that this classification is finalized. Last year, I attended an academic conference on provincial disease control and argued with a group of veteran experts for half an hour. An old director who has been involved in chronic disease prevention and control all his life said that many screening tests have already passed the level two level, and we cannot stick to the definitions in the textbooks. Take the pre-marital thalassemia gene screening as an example. It checks whether both spouses carry the thalassemia gene. If both of them are carriers, they will provide fertility guidance and even recommend prenatal diagnosis to prevent the birth of children with severe thalassemia from the root cause. This kind of screening does not look for people who are already sick at all. It directly eliminates the possibility of disease at the cause stage. It makes perfect sense to say that it is an extension of primary prevention. There is also a tuberculin test for school-age children. If a strong positive result is detected but the disease has not yet occurred, preventive anti-tuberculosis treatment will be given directly. In essence, it will block the cause of the disease when they are not sick. Many front-line disease control personnel assume that this kind of screening is a supplement to primary prevention.

There is another type of screening that is less controversial, which is complication screening for people who have already had the disease. Many clinicians directly classify it as tertiary prevention. I used to go to the outpatient clinic with a friend from the endocrinology department, and I met an old man who had been suffering from diabetes for 10 years. He followed the doctor's instructions and did fundus and urine microalbumin screening every year. The year before last, he was found to have microaneurysm in the fundus. He had laser treatment as soon as the lesions appeared. Now his vision is almost the same as that of normal people. If we wait until he is out of sight before treating him, there is basically no room for recovery. This kind of examination, which screens patients who have been diagnosed for complications in order to avoid aggravation of the disease and reduce the rate of disability and death, is exactly in line with the core goal of the third-level prevention of "treating diseases, preventing disability, and improving the quality of life", and it is completely reasonable to classify them as third-level.

In fact, during the five or six years I have been working in public health, I rarely talk to the people who come for screening about the levels of prevention. Classification is essentially a tool we use when designing projects and evaluating effects. When implemented, no matter what level of screening it is, it can make people suffer less, spend less money, and prevent serious diseases in front of them, which is better than anything else. Last time, an old man heard about free colonoscopy screening from the community. He didn't want to come because it was too troublesome. I told him that if the polyps were detected early, he would not get bowel cancer if the polyps were removed. He immediately signed up. You see, people are always more concerned about the real benefits than professional classification.