Not being an expert, I gave the title of a book written by a neurologist who specializes in dementia. He tells, in his book, how to go about getting the correct diagnosis. And he himself follows certain strict proceedures to arrive at a diagnosis for Alzheimer's. I actually got the impression that he's overly cautious in this regard. But he's a doctor and I'm not.
When I took my father to a general practitioner, he got the correct diagnosis of "Alzheimer's" in about 5 minutes. Was the doctor 100% sure of his diagnosis? No, because when it comes to complex health issues like dementia, there's seldom 100% certainty, at least by a general practitioner who only spends five or 10 minutes with the patient. But the doctor did tell us that we could have certain other tests done to eliminate other possible causes. So we did and couldn't find any other cause.
The first thing that we noticed that was not normal was her confusion, repeating herself, forgetting, and very strange behavior. She did go through a battery of tests and after all that was done she was diagnosed with vascular dementia.
That's what they do, they rule all possible causes out, and then determine if they have alzheimers/dementia.
There are a lot of forms of dementia out there including nutritional dementia, and medication related dementia which are reversible in the beginning unlike some of the more serious forms. Since a cause hasn't been found, hopefully your father will get better instead of worse. Maybe he is suffering from age related senility?
Death and autopsy of the brain is the only absolute way to make diagnoses of Alzheimer's. Meanwhile the only way to be somewhat positive is by ruling out things. Testing for other things that cause dementia. A detailed medical history of the patients life and the aid of Brain scan and other blood tests will rule out other things. Often times doctors will just call it Alzheimer's because there is money these days (by the Feds and states)being dumped into that diagnosis and nursing homes/health care facilities have built special locked units for the Alzheimer's and the only way to be admitted is if the patient has that as primary diagnosis. So not all that are diagnosed actually have it but it is a diagnosis to have if you need to put someone that because of confusion wander or run away from an unlocked facilities. There is no absolute yet to know for sure in a living patient if it is Alzheimer's...just an educated guess.
I like your "10 Signs of Alzheimer's". My father had every one of those signs. But I believe there's at least one more sign: Lack of sense-of-smell could be the very first sign. My father lost his sense of smell many years before there were any other symptoms. We just thought it was odd that he couldn't smell a pile of leaves burning or cookies baking in the oven and we didn't make any connection to dementia or Alzheimer's disease.
I anticipate that someone will want to tell me that it doesn't always mean that someone has dementia in their future. That's true. However, if I lose my sense of smell late in life, like my father did, I don't see how I could help but draw that conclusion. Assuming I remember to draw that conclusion.