– Retinol Binding Protein 4 (RBP4) is a member of the Lipocalin family and in the blood. RBP4 is the specific vector for retinol. RBP4 is expressed and secreted by adipose tissue, and is associated with insulin resistance. RBP4 delivers retinol from the liver stores to the peripheral tissues. In plasma, the RBP-retinol complex interacts with transthyretin to prevents its loss by filtration through the kidney glomeruli. Defects in RBP4 cause retinol-binding protein deficiency and can cause night vision problems.