Abstract: The present invention relates to a Raman spectroscopy method for determining protein structure associated with global cognitive deterioration in Alzheimer's disease from the Raman spectroscopic analysis of a human blood sample, preferably of a human blood plasma sample, comprising obtaining at least one spectral value of at least one of the Raman spectrum regions comprised between 1600-1700 cm?1, between 910-980 cm?1, between 730-760 cm?1 and/or between 390-450 cm?1, and where said spectral value allows obtaining an indication of the presence or absence of protein structure associated with a condition of Alzheimer's disease. The present invention also relates to a method for the infrared spectroscopic analysis of a blood sample, by means of additionally obtaining at least one spectral value of at least one of the infrared spectrum regions comprised between 1600 and 1700 cm?1, and/or between 1000 and 1150 cm?1 and/or between 1140 and 1190 cm?1.