You assume that given a positive result you can gain certainty, but that is not so. Medicine is a statistics game, even for individuals with test results, and e

You assume that given a positive result you can gain certainty, but that is not so. Medicine is a statistics game, even for individuals with test results, and even when adding even more tests on top you don't turn it into certainty. What is abnormal for somebody else may be normal for your body, and trying to do something about it may actually be worse. Weighing risks and benefits sounds easy, but it only really works for doctors (looking to optimize their overall success for all their patients) rather than for individuals - for large numbers. Plus, it's always based only on the "known knowns". There is a huge amount of "known unknowns", and the amount of "unknown unknowns" is unfathomable (thanks Rumsfeld, famous American philosopher, for popularizing those terms). What is "normal" is not based on a complete understanding of every individual as a complete system but the parts are compared among individuals after abstracting away the context that they are in. So knowing what is "normal" or not does not give you nearly as much information as you may like. Sure, your method works for a lot of cases - but it doesn't work or not very well for orders of magnitude more.