The technique, which is noninvasive, fast, and low-cost, measures how much infrared radiation is either emitted or absorbed by white blood cells and measured by spectroscopy.

Scientists at the Instituto de Estructura de la Materia (Madrid, Spain) used two-dimensional infrared spectroscopy to measure and compare the infrared radiation emitted or absorbed by the leucocytes of healthy controls, versus those of patients with mild, moderate, and severe Alzheimer's disease. A total of 50 patients with Alzheimer's and 20 healthy controls took part in the study and gave blood samples. The white blood cells or mononuclear leukocytes are thought to carry amyloid-ß peptide in Alzheimer patients.

The infrared spectrum of the film of leucocytes was measured with a 1725X spectrophotometer (Perkin-Elmer; Waltham, MA, USA) with high resolution and obtained as an average of 32 scans. The scientists found significant differences in the range of infrared wavelengths displayed between subjects, which were attributable to the different stages of formation of amyloid-ß structures in the blood cells. The results showed that, with this method, healthy controls could be distinguished from mild and moderate sufferers of Alzheimer's disease. The method is being explored as a tool for early diagnosis.

The analysis showed a good test performance: 90% sensitivity and 90.5% specificity for determinations involving mild and moderate AD patients and age-matched healthy controls, and 82.1% sensitivity and 90.5% specificity for determinations involving patients at the three AD stages, mild, moderate, and severe, and age-matched healthy controls. The study demonstrated that AD is associated with higher percentages of β-structure in mononuclear leukocytes than those in healthy age-matched controls.

The authors concluded that the method they used could potentially offer a more simple detection of alternative biomarkers of Alzheimer's disease. Mononuclear leukocytes seem to offer a stable medium to determine ß-sheet structure levels as a function of disease development. The measurements seem to be more sensitive for earlier stages of Alzheimer's disease, namely mild and moderate. The study was published online on January 21 2012, in the journal Analytical and Bioanalytical Chemistry.

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