A device for preparing a blood sample, including a microfluidic card including: a first chamber for separating and/or extracting proteins to be analyzed that are present in the blood sample; a second chamber used for an operation involving digestion of proteins of different species that are present in the sample, to obtain a second sample containing digested peptides and nondigested proteins; and a third chamber connected to the second chamber to receive the second sample containing the digested peptides and the non-digested proteins, the third chamber being used for an operation involving purification and stabilization of the digested peptides.