SCD patients and healthy subjects can be individualized on the basis of the metabolic information contained in their RBCs. PCA score plots for RBC extracts obtained from 28 SCD patients and 24 controls. Each point (red triangles and green squares for SCD patients and healthy subjects, respectively) represents an LC/MS metabolic fingerprint. (A) Data acquired in the negative mode of electrospray ionization. The variables contained in the resulting data matrix were mean-centered and scaled to unit variance before PCA. The separation occurs on the first component. (B) Data acquired in the positive mode of ionization. The variables contained in the resulting data matrix were mean-centered and scaled to Pareto variance before PCA. The separation occurs on the second component. (C-D) Impact of the storage of RBC extracts on the metabolic information contained in the LC/MS fingerprints. Blood samples from SCD patients and controls (9 patients, and either 11 or 5 controls, for positive or negative ion mode, respectively) were collected and divided in 2 aliquots, one being immediately extracted and the other frozen,²³  before future extraction. (C) PCA scores plot observed with detection in the positive ion mode. (D) Correlation between concentration ratios of SCD patients to controls obtained on fresh and frozen RBC extracts on 34 discriminating metabolites detected in positive ion mode.