It does, however, provide a reasonable degree of confidence. The blood usually carries messages of ill health before such a condition could be detected by any other method. The CA profile is a very powerful tool as a part of a diagnostic workup. A positive value may suggest, sometimes strongly, the presence or the process of developing a cancer. The tests, in general, are not organ-specific.
Normals vary by age.
I felt very uncomfortable making people radioactive for the tests, touching the radioactive materials, and having to be near the radiated, injected people. The doses used were well within acceptable limits by all regulatory agencies. However, I have always maintained there is no such thing as safe radiation. It is made up of various tests. It is not invasive or radioactive.