They are right, there is no test that will prove 100% that you have IBS.IBS is diagnosed based on symptoms and testing for other things when needed.Do you have the symptoms of IBS (or other functional bowel disease)?Do you have any symtoms that indicate something other than IBS is likely? Some of that is the "minimal" blood tests they do. If the blood tests are abnormal that triggers additional testing. Pretty much if you are otherwise normal with just IBS symptoms you are going to get an IBS diagnosis.These days most doctors feel spending thousands of dollars and weeks of your time with multiple bowel cleansing when they are near certain none of them will find anything is a waste of effort, and there is evidence the only thing you do for these patients is make the IBS worse from the stress of coming in again and again for test after test that shows normal results.How many normal tests would it take you to believe it is IBS? Some people will never ever believe it because it isn't a number on a chart and do end up making themselves a lot worse off than they are trying to get some proof it MUST be something else.If you have symptoms of IBS and do not have symptoms of other things, and your minimal tests are normal or your tests that were done because of the symptoms that could be something else are normal, then they can diagnose you with IBS.Really we think everything else is so clear cut and there is the one perfect test that is the one thing that gives a diagnosis, but it really is not that straight forward for most things. Yep somethings are really clear cut, but a heck of a lot are just as murky and muddy as IBS. Even when it appears clear cut there are any number of confounding factors that make it difficult to figure out what is going on.I wish the doctors could stick a thingy on your body and prove to you that you have it, but they do not.They do know that patients with clear symptoms of functional bowel symptom problems with normal blood tests and no "red flag" symptoms of other disorders generally don't have anything besides a functional bowel disorder.The GI doctor may not do any more tests than the general doctor, most of the tests they would run for other things regular doctors will have done if you need them. You may not get whatever it is you think you need from a GI specialist if the regular doctor has done their job. Some GI doctors are better at helping patients figure out what works for them, so it can be worth seeing one, but they don't have a magic machine that proves to a patient they have a functional GI disorder. K.