well, Lucci, your questions is actually the point here: there ARE no tests to prove Alzheimer's. In fact, a recent article on this site detailed how forensic investigation into the brains of 211 people diagnosed with a dementia of the Alzheimer's type (DAT) showed that 50 percent of those brains had NO signs of plaques and tangles (considered to be the only sure sign of alzheimer's).
closely involved with the alzheimer's world for about 25 years now, i'd say that alzheimer's itself is one of the least provable menifestations of dementia. it's just become a useful dark name to scare up contributions to the Alzheimer's Association and make prescription medications.
and, yes,JayR76, you are very right. people are terrified of alzheimer's (and that's what happens when you try too many bad ways to scare up contributions) and do much better with the word dementia, which after all is much more accurately used than the term alzheimer's.
in my workshops, i just say: remember, all alzheimer's is dementia but by no means all dementia is alzheimer's. in fact, as far as i see, less and less dementia is alzheimer's.
as Paula said, "dementia" is both a general description of observed symptoms (short-term memory issues, cognitive failures and so on) and also used in specific condition names -- vascular dementia, Lewy Body. that makes it confusing for everyone.
just to help out, there are about 50 different dementias of old age, plus dementia behavior can arise out of many other health conditions.
so, that's why we're all confused about everything in the dementia world.