Star Trek’s Dr. McCoy had no problem finding out what ailed his patients. He simply waved a handheld scanner over them, and the tricorder spat out a diagnosis — even if the patient was a Romulan.
Earthbound diagnostics haven’t yet measured up to the extragalactic version, alas. Go to the doctor, and it’s likely to take a variety of tests to come up with a diagnosis. And even then, the cause may still elude the experts.