The most important part of making a diagnosis is to obtain accurate information from close family members and friends who know the patient well. We need to establish that a decline in a level of functioning has occurred that cannot be explained by depression or systemic illnesses such as renal or heart failure, and that the process is progressively worsening. The baseline of each individual is unique and determines the level with which we establish if there has been a deterioration.
A urinary tract infection can cause major confusion in an elderly person and should not be labeled as dementia. Pneumonia, head trauma and medication side effects often cause memory problems too, but patients get better over time and as such they do not meet the diagnostic criteria for dementia.
Memory problems are ubiquitous and by themselves are not worrisome for the onset of dementia. We all forget our keys, may have difficulty finding our car in the parking garage, or walk into the basement and not remember why we went there. Memory problems are concerning, and a sign of dementia, when a patient forgets major events, names or things that are significant. Not showing up at a daughter's wedding, forgetting names of grandchildren or not remembering how to drive are concerning enough to warrant a dementia evaluation.