The idea is to go see your doctor when you have symptoms. If you go see your doctor every time some parameter is out of what you consider to be your personal error bands you'd be spending all day in the doctors office. Tests are useful to rule out things you don't have and to close in on the things that you do have once you have something that doesn't function well enough to notice. Until then it is a waste of resources to spend a ton of money and capacity on testing people without symptoms. Eventually those will clog up the system to the point where those that do need medical attention will end up without it.