The search for diagnostic and prognostic markers in Alzheimer's disease (AD) has 
been an area of active research in the last decades. Biochemical markers are 
correlates of intracerebral changes that can be identified in biological fluids, 
namely: peripheral blood (total blood, red and white blood cells, platelets, 
plasma and serum), saliva, urine and cerebrospinal fluid. An important feature 
of a biomarker is that it can be measured objectively and evaluated as (1) an 
indicator of disease mechanisms (markers of core pathogenic processes or the 
expression of downstream effects of these processes), or (2) biochemical 
responses to pharmacological or therapeutic intervention, which can be 
indicative of disease modification. Platelets have been used in 
neuropharmacological models since the mid-fifties, as they share several 
homeostatic functions with neurons, such as accumulation and release of 
neurotransmitters, responsiveness to variations in calcium concentration, and 
expression of membrane-bound compounds. Recent studies have shown that platelets 
also express several components related to the pathogenesis of AD, in particular 
to the amyloid cascade and the regulation of oxidative stress: thus they can be 
used in the search for biomarkers of the disease process. For instance, 
platelets are the most important source of circulating forms of the amyloid 
precursor protein and other important proteins such as Tau and glycogen synthase 
kinase-3B. Moreover, platelets express enzymes involved in membrane homeostasis 
(e.g., phospholipase A2), and markers of the inflammatory process and oxidative 
stress. In this review we summarize the available literature and discuss 
evidence concerning the potential use of platelet markers in AD.