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I ouce asked on Quora, why people do not do yearly blood tests and imaging, to prevent getting stage 4 cancers.

The answers listed reasons not to do this:

  1. It would cost a lot of money (for the country, the person, or insurance companies)
  2. No Symptoms, No tests needed (but cancer could exist even without symptoms, right ?)
  3. Use preventive medicine tests from your own money
  4. Other financial reasons

Why do we think it's a waste of money to do a test, when it's something we can do once each year, so we don't spend much more money in the future curing from killer diseases?

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Screening tests such as "blood tests and imaging" have two costs and one benefit:

  • the cost (dollars and possible health problems) of the actual screening, which can in some cases be free
  • the cost (dollars and possible health problems) of the followups required when the screening is positive
  • the benefit of less people dying or their treatment being less expensive when things are found before there are symptoms.

Obviously, deciding whether or not to screen will be different for every disease because each of these costs and benefits will be different for every disease. But it's really important to realize that screening brings false positives. These cause distress and anguish to people who believe they are dying and they cost a lot of money because the investigations required are expensive and intrusive.

Recently Ontario has stopped recommending women do monthly breast self exams. These are free. However they do not save any lives. Women who actually have lumps find them without dutifully checking every month or week for them. But with the regular screening, many find things that are not cancers. They need to take time off work, get biopsies, which can be inconclusive, get scans, even have surgery to remove lumps so they can be sent to pathology, and so on. This costs a lot of money directly to the hospital and indirectly in people being off work. All this expense is pointless: there is no difference in survival rates between groups who do BSE and those who do not. They didn't even take into account the misery of thinking you have cancer when you don't.

(A news article about the changes, which also includes not having doctors do breast exams routinely if there are no symptoms, and not having mammograms before age 50. The Task Force Guidelines referred to in that article.)

For screenings that are not just self-examination, consider also the radiation from scans, the chances of an allergic reaction to contrast dye, the chances of infection from a blood test, of catching an antibiotic-resistant infection while in the hospital recovering from having something removed, and so on. Both the screening and the procedures that happen when someone screens positive can hurt or kill people if you screen everyone, meaning millions of people.

Finally, while it may seem logical to you that screenings like this would save lives by catching things earlier, there is very little evidence to support that. Our bodies actually destroy small cancers all the time: just because you see a small cancer on a scan doesn't mean the huge treatment machine has to swing into action. That is only needed when a small cancer demonstrates it's becoming a big cancer. And in the majority of cases, there are symptoms. These things get found.

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    Great answer. You might add that making a decision on whether to recommend screening tests for the entire population is different from deciding whether to screen an individual patient. At the population level, cost-benefit and risk (like number needed to harm) are extremely important. At the individual level, individual considerations must be taken into consideration. That is why it takes a clinician to discern whether or not to do a non-recommended screening test (or not do a recommended screening test). – DoctorWhom Aug 26 '17 at 6:43
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Great answer above. This is to add on to it:

Making a decision on whether to recommend screening tests for the entire population is different from deciding whether to screen an individual patient. The USPSTF uses panels of experts who employ extensive epidemiology and biostatistics and literature reviews to make those recommendations.

At the population level, things like cost-benefit analysis, how rare a condition is, how many you need to screen before you prevent 1 cancer, and risk (like what % of screening tests result in harmful outcomes) are extremely important.

This is reflected in the Grades.

Grade C recommendations = Consider offer or provide this service for selected patients depending on individual circumstances.

"recommends selectively offering or providing this service to individual patients based on professional judgment and patient preferences. There is at least moderate certainty that the net benefit is small."

Grade D recommendations = Discourage the use of this service.

The USPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.

At the individual level, like grade C, individual considerations must be taken into consideration. That is why it takes a clinician to discern whether or not to do a non-recommended screening test (or not do a recommended screening test).

Also, once someone presents with a suggestive symptom, doing a test is not a considered a screening test but a diagnostic test. Once someone is extremely anemic, the appropriate workup for anemia isn't screening, it's diagnostic. The recommended workup steps for symptoms/signs/findings are established by consensus of experts based on research. That's another topic.

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