They won't say, "My doctor said I have this, but I have my doubts." That's because they know physicians are human; if your doctor is extremely respected in the field and I know you're hoping that I'll find a different diagnosis than he did, that could unconsciously affect the way I look at the test results. Instead of just giving my neutral and independent opinion on the data, I'll almost have to examine the clues and rationale an esteemed professional used to come to a specific conclusion, and that's not quite the same (you don't want your first doctor's work to be checked; you want another physician to approach your case completely fresh, without any preconceived notions).
For obvious reasons, never bash their first doctor or the testing procedures when getting second opinions, or brag about him and how you're sure he's correct (the latter can happen when patients getting a second opinion only to satisfy an insurance requirement).
Just give the facts and have an honest, objective conversation about those facts. In short, avoid saying or doing anything that could bias our interpretation of their history, condition or test results. This doesn't mean you need to cloak everything in secrecy; just don't make it known that you came to us with the specific intent or hope of getting a specific answer.
Also, ask your second-opinion doctor what specific information he'll need. Happily, you probably won't need to retake the same battery of tests you went through to get the first diagnosis; the second doctor may be able to interpret the results you already have. He should give you a basic exam, though, and you'll need to tell him your health history and other important points.
Find out more about this book:YOU: The Smart Patient: An Insider's Handbook for Getting the Best Treatment