Vascular endothelial growth factor (VEGF) is a 27KDa signaling protein produced by cells that stimulates vasculogenesis and angiogenesis. The VEGF family includes VEGF-A (VEGF), VEGF-B, PlGF, VEGF-C and VEGF-D. VEGF is a heparin binding protein and exists as a disulfide linked homo-dimer. It has at least 6 isoforms produced by alternative splicing. The Simoa Human VEGF assay detects the 165 amino acid form of the factor (VEGF-165), which is the most common form in tissues. VEGF induces endothelial cell proliferation, promotes cell migration, inhibits apoptosis, and induces permeabilization of blood vessels. Though VEGF acts primarily on endothelial cells, it also binds to receptors on HSCs, monocytes, osteoblasts and neuronal cells. VEGF is also involved in vasodilation through induction of endothelial nitric oxide synthase and the subsequent increase in nitric oxide production. Serum concentration of VEGF is high in bronchial asthma and diabetes mellitus. When VEGF is over-expressed, it can contribute to disease; cancers that can express VEGF are able to grow and metastasize.