Electrophoresis V.S Western Blotting for detection of a protein

So after some intense dialog with the Biker Scout and C-3PO I think that I may be a bit closer to a project idea, even though it seems very far away from my goal upon first glance. This semester I will be using electrophoresis to isolate a specific protein. I will then use western blotting to introduce antibodies to the protein. Once I become fluent in this process my hope is to actually go after more specific human proteins/antibodies. I am curious to know if the antibodies produced from the beta amyloid protein could be used to create a test that would show the varying degree of beta amyloid proteins if they were present in an individual's blood.  The first question that I had was; "Can beta-amyloid proteins be detected/isolated from urine and/or blood"? The answer is yes, they can be detected in blood, cerebral spinal fluid, and urine. My next question was,"Why is there not an inexpensive urinalysis (the least invasive procedure for the patient) that could detect the amount of beta amyloid proteins excreted through urine"?  If the theory of the accumulation of these proteins or plaques is what causes the cognitive decline associated in Alzheimer's Disease  is correct, than why are we not incorporating a device that will detect these plaques BEFORE they have time to build up? Many health care professionals already incorporate urinalysis into their annual physical protocol, why are we not monitoring the production of these proteins? Currently, the testing for these proteins is extremely costly and is almost always done on individuals that are ALREADY experiencing cognitive decline. I guess what I am asking is; when will we start to become proactive and get ahead of this disease, instead of ignoring it until it takes up space in our heads?