PCSK9 is a novel target in cholesterol-lowering therapy. PCSK9 plays a major regulatory role in cholesterol homeostasis by membrane LDL-Receptor levels reduction. Finally, the metabolism of LDL-particles is decreased which may lead to hypercholesterolemia. The PCSK9 inhibitors (PSK9i) are a newer class of injectable drugs that have been shown to dramatically lower LDL cholesterol levels. The determination of PCSK9 levels is obviously of great diagnostic as well as treatment monitoring importance. Sandwich ELISA is the most frequently used immunoassay format for the detection of proteins. The main features of those immunoassays are high sensitivity and specificity. The use of a biotin-labeled detection antibody in combination with a streptavidin-peroxidase conjugate is a way how to improve the ELISA sensitivity reaching as low detection limit as sub pg/ml level.