Influence of blood sampling on protein profiling and pattern analysis using matrix-assisted laser desorption/ionisation mass spectrometry

To describe the influence of blood sampling/sampling tubes on mass spectrometric and clustering results, and on clinical blood variables, in blood samples collected from healthy volunteers and patients with prostate cancer. Two venous blood samples were taken from 12 healthy volunteers and 12 patients with localized prostate cancer. Two blood samples were taken from each participant using two different venepuncture systems (group A and group B). The Kolmogorov-Smirnov test was used to identify the peaks distinguishing the different groups. In a 10-fold cross-validation study, decision trees for identifying discriminatory peaks that separate the benign from the malignant were constructed. The decision tree separated samples measured by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) from healthy volunteers from those of patients with prostate cancer, with a sensitivity of 93.6% and a specificity of 91.6%. Of special interest is that one peak at 6941 m/z was produced during blood sample preparation and had a very powerful influence on the results of the classification. The results clearly showed that blood-sampling systems have a great influence on the recorded MALDI MS traces, and thus can markedly influence and confound the results of the MS analysis, whereas clinical variables might remain unchanged. MS profiling is a promising method of marker discovery, but as it could be shown well-designed studies are critical to allow proper interpretation for the identification of key variables as well as for the clinical use.