| Use: | Retinol binding protein (RBP) is responsible for binding and transporting retinol (vitamin A). It has a binding site for one molecule of retinol and circulates in the plasma together with prealbumin in the form of a protein complex in a molar ratio of 1:1. This binding to prealbumin prevents greater glomerular losses of the retinol-binding protein. Only the retinol-free form of the retinol-binding protein, which has no affinity for prealbumin, undergoes glomerular filtration unhindered as a result of its low molecular weight; it is re-absorbed by the tubular cells and catabolized there. This explains the elevated serum level of retinol-binding protein in advanced chronic renal insufficiency. Since retinol-binding protein and prealbumin are synthesized in the liver, their serum concentrations are reduced in acute and chronic hepatic diseases. Decreased concentrations have also been observed in cystic fibrosis. Due to the short half-life of RBP (11 hrs), it is an excellent indicator of early malnutrition (half-lives: albumin 21 d, pre-albumin 2 d). |
