Retinol-binding protein that mediates retinol transport in blood plasma. Delivers retinol from the liver stores to the peripheral tissues. Transfers the bound all-trans retinol to STRA6, that then facilitates retinol transport across the cell membrane. Interacts with TTR. Interaction with TTR prevents its loss by filtration through the kidney glomeruli. Interacts with STRA6. Highly expressed in liver. Also expressed in adipose tissue (PubMed:23719693). Expressed by endometrium from days 16-25 and by unattached chorioallantois from days 30-36 during pregnancy (PubMed:2015342). Secreted in fetal fluids. Present on day 25, decreases from days 30-39, and disappears by day 50. Expressed by blastocysts on days 10-25 during prenatal development, but disappears by day 50. Belongs to the calycin superfamily. Lipocalin family.