Which level of prevention does disease screening belong to?

The current mainstream consensus in the field of public health is that disease screening belongs to the category of secondary prevention, but there are also a few different views in academic circles and in practice.

The core of secondary prevention is the three early principles of "early detection, early diagnosis, and early treatment". It is aimed at the stage when the disease has occurred but has not yet shown obvious clinical symptoms. In essence, it is to conduct regular demining of the body. When it is not exploded, it is better to find and dismantle it than to repair it after it is exploded. The two cancer screenings we usually come into contact with the most, low-dose lung cancer CT screening for people over 40 years old, and colorectal cancer occult blood screening kits distributed free of charge in the community all fall into this category. I also met an aunt when I was doing screening education in the community last month. She took part in the free cervical cancer screening last year and found precancerous lesions. She fully recovered after a minor surgery. If she had to wait for the symptoms of contact bleeding to appear before going for a check-up, it might be delayed to the mid-to-late stage, and the difficulty and cost of treatment would be several orders of magnitude higher.

As for the existing controversies, they mainly focus on a few special screening items: such as neonatal phenylketonuria screening. As long as the screening test is positive and the child is fed a special low-phenylalanine formula food from an early age, the child will not develop typical disease manifestations such as mental retardation and developmental abnormalities, which is equivalent to blocking the onset of the disease from the root. Therefore, a few scholars believe that this kind of screening, which can directly avoid the disease, can also be included in the category of primary prevention.

However, when we usually do grassroots public health operations, we basically classify all screening items into the assessment items for secondary prevention. After all, most screenings are still intended to detect early-stage lesions that already exist. This special situation is just an example. To be honest, classification is originally intended to facilitate work, and the core purpose is to help everyone avoid suffering and spend less money.