You know whether or not it's warranted before you run the test. That's the whole point of the discussion around when preventative testing is appropriate. The ke

You know whether or not it's warranted before you run the test. That's the whole point of the discussion around when preventative testing is appropriate. The key is that the test is just one additional data point. Before running the test - you want to make sure that the data from the test will be useful for whatever purpose you want the test for (false positives could be ok if the point is to minimize false negatives). That way when you run the test, it's always "warranted" to follow up if needed. We do mammograms for healthy seeming people all the time - it's totally feasible that we'll determine that these new approaches are informative enough to become recommended for the general public, but we're still on that scientific journey