This becomes even more true when you consider there is risk to every test. Some tests have obvious risks (radiation risk from CT scans, chance of damage from spinal fluid tap). Other tests the risk is less obvious (sending you for a blood test and awaiting the results might not be a good idea if that delays treatment for some ailment already pretty certain). In the bigger picture, any test that costs money harms the patient slightly, since someone must pay for the test, and for many the money they spend on extra tests comes out of money they might otherwise spend on gym memberships, better food, or working fewer hours - it is well known that the poor have worse health than the rich.