Early signs of Alzheimer's disease could one day be diagnosed using a simple blood test, a pilot study suggests.
Scientists showed how healthy volunteers, and people with mild and moderate Alzheimer's, could be distinguished by exposing their blood to infrared light.
The test relies on differences between patterns of infrared light emitted or absorbed by white blood cells.
This depends on levels of amyloid beta peptides - protein building blocks - in the cells.
Amyloid beta builds up in the brains of Alzheimer's patients and is a key hallmark of the disease. The research shows that the molecules are also carried in white blood cells.
Scientists in Spain, who tried the technique out on 50 patients with Alzheimer's and 20 healthy participants, found "significant differences" in the range of infrared wavelengths displayed by the samples. These were attributed to different stages of amyloid beta formation in the cells.
The scientists, led by Dr Pedro Carmona, from the Instituto de Estructura de la Materia in Madrid, wrote in the journal Analytical & Bioanalytical Chemistry: "The method we used can potentially offer a more simple detection of alternative biomarkers of Alzheimer's disease..
"Our measurements seem to be more sensitive for earlier stages of Alzheimer's disease, namely mild and moderate."
Dr Anne Corbett, research manager at the Alzheimer's Society, said: "This study gives us more information about proteins that change during the early stages of Alzheimer's disease.
"The research builds on current evidence that we may one day be able to identify people with Alzheimer's disease through a simple test. This could also have positive implications for a more accurate diagnosis. More research is now needed.
"We do not know whether the changes to the proteins are a cause or a symptom of the disease or whether they can be detected before symptoms develop."