1. The document describes a study analyzing serum protein profiles from 15 individual samples using online two-dimensional low-flow liquid chromatography-tandem mass spectrometry (LC-MS/MS). 2. Over 400 proteins were quantified across the samples, with 237 proteins showing at least a two-fold change in abundance between samples. 3. Principal component analysis separated the samples obtained from one source, indicating the impact sample preparation can have on protein profiles. Deeper profiling of individual samples is needed for precision medicine applications like biomarker discovery.