There are 2 forms of Pregnancy-associated plasma protein A (PAPP-A), one is heterotetrameric and produced by placental syncytiotrophoblast cells during pregnancy, and another is a homodimer secreted by vascular cells. PAPP-A secreted by vascular cells is a high molecular weight, zinc-binding metalloproteinase that is associated with vulnerable plaques and is a marker of adverse outcomes in both acute coronary syndrome and stable coronary disease. Serum PAPP-A level can be measured using a quantitative two-site sandwich immunoassay.