Phospholipids are a major component of lipid bilayer membranes. In addition, phospholipids are biologically important molecules as they are closely involved in signal transduction. Most phospholipids contain one diglyceride, a phosphate group, and one choline moiety. In human serum and plasma, almost 95% of the phospholipids are choline-containing phospholipids such as phosphatidylcholine and sphingomyelin. The remaining 5% is mainly choline-free phospholipids (i.e. phosphatidylethanolamine and phosphatidylserine). Phospholipid concentration is considered a disease biomarker as it can be altered in many lung, liver and heart diseases.