Plasma concentrations of glutamate and its metabolites in patients with Alzheimer's disease.

Neurologic and psychologic tests without brain tissue biopsy do not establish the diagnosis of Alzheimer's disease. This pilot study demonstrates significant increases in the activity of plasma glutamate dehydrogenase and the plasma concentrations of aspartate, glutamate, and alpha-ketoglutarate in nursing home residents with previously diagnosed Alzheimer's disease when compared with that in other nursing home residents without Alzheimer's disease who had no complicating conditions. Plasma concentrations of gamma-aminobutyric acid, glutamine, and activities of plasma glutamate decarboxylase, glutaminase, and glutamine synthetase were not significantly different in the two groups. A discriminant analysis number, based on the four significantly different compounds, is obtained that may be used as the basis for an inexpensive, non-invasive, and accurate screening test for Alzheimer's disease.