Lipoprotein (a) (Lp (a)) is a particle composed of lipids and proteins; a portion of this particle consists of phospholipids, cholesterol and a specific apolipoprotein, apolipoprotein B100, identical to LDL (low-density lipoprotein), which transports cholesterol. The other part is an apolipoprotein (a) linked to apolipoprotein B100 by disulphide bridges. Apolipoprotein (a) (not to be confused with apo A1) is specific to Lp (a) and is synonymous with increased cardiovascular risk. There is no known specific function for Lp (a). It is possible that Lp (a) acts as an acute phase protein. It is therefore preferable to determine the level in the absence of an inflammatory reaction. The concentration of Lp (a) seems, for a very large part, genetically determined; the indication for determining the Lp (a) level occurs when screening for cardiovascular risk (coronary artery atherosclerosis). It appears that Lp (a) increases the risk of heart disease either by competing with plasminogen for binding sites on blood clots or by causing atheroma formation.