There are no laboratory tests available that will positively diagnose Alzheimer’s disease. Currently, the only definite diagnosis of AD is to microscopically examine a section of the patient’s brain tissue after death. Pathologists look for senile plaques and neurofibrillary tangles characteristic of AD. Since plaque and tangle formation is also seen in normal ageing, the sample must be compared to a control sample (normal, non-AD brain tissue) from a person the same age as the patient.
However, doctors currently use a variety of tests and procedures to rule out other causes for dementia, such as anaemia, infection, disorders of the thyroid gland, or vitamin B12 deficiency, before diagnosing patients with ‘possible AD’ (meaning that the dementia could be due to another cause, such as a stroke). A hallmark of Alzheimer‘s disease is that it’s appearance is a subtle, progressive decline in function. If the onset of the patient’s problems is abrupt or happened in a step-wise fashion, then the cause is most likely something other than AD.
When a patient presents with symptoms of dementia, the doctor will evaluate his or her personal and family history (preferably of several generations); perform a physical examination; determine the age of onset, and give the patient neuropsychological tests to measure his or her memory, language skills and other cognitive functions. In some cases, computed tomography (CT) or magnetic resonance imaging (MRI) scans may be used to look for evidence of trauma, tumours or stroke that could be causing dementia and to look for brain atrophy (shrinkage, usually only seen later in the Alzheimer‘s disease progression). There is a lot of ongoing research looking for biomarkers in both blood and CSF that can be used to either diagnose Alzheimer’s disease accurately or even predict which people may develop the disease in the future. However no such tests are available yet.