osteocalcin

noun

os·​teo·​cal·​cin -ˈkal-sən 

: a protein that is found in the extracellular matrix of bone and in the serum of circulating blood, is produced by osteoblasts especially in the presence of vitamin K but is not a collagen, and when present at excessive levels in serum may be indicative of various disorders (as Paget's disease or postmenopausal osteoporosis) of bone metabolism