The DetectX^® Retinol Binding Protein (RBP) Multi-Format ELISA Kit is designed to allow for the measurement of both high and low RBP levels in a variety of samples including dried blood spots, serum, EDTA and heparin plasma and urine with the same kit. The kit uses native human RBP as a standard. Standards or diluted samples are added to a coated microtiter plate along with a RBP-peroxidase conjugate and the binding reaction initiated by addition of a RBP-specific sheep antibody. After a 60-minute incubation, the plate is washed and TMB substrate solution added. After 30 minutes, the color development is stopped and the intensity of the generated signal is read at 450nm.

Retinol binding protein (RBP) is from a family of structurally related proteins that bind small hydrophobic molecules such as bile pigments, steroids, odorants, etc. RBP is a 21 kDa highly conserved, single-chain glycoprotein, consisting of 182 amino acids with 3 disulfide bonds, that has a hydrophobic pocket which binds retinol. In urine RBP has been shown to be a useful marker for renal function as it is totally filtered by the glomeruli and reabsorbed by proximal tubules. This has made RBP a tool to study renal function in heart or kidney transplant recipients, type 1 and 2 diabetics, and in people exposed to uranium from mining operations.  Modulating RBP4 levels may lead to new strategies in treating type 2 diabetes

When in serum, the majority of RBP bound with retinol is reversibly complexed with transthyretin. This complex transports retinol to specific receptors of various tissues in the body.  Vitamin A status is reflected by serum concentration as it is homeostatically controlled and does not fall until stores are drastically reduced.  RBP has been shown to be a useful surrogate marker for retinol because of the correlation between retinol and RBP in serum, which implies that RBP may be used to monitor vitamin A deficiency (VAD). The WHO has estimated that 250 million children have moderate to severe VAD due to lack of adequate nutrition, and the rising cost of food staples around the world further exacerbates this problem.  In addition to nutritional deficiencies, infectious stresses have been shown to depress retinol concentrations and individuals with diseases such as cystic fibrosis and HIV-1 also run the risk of VAD due to the infectious stresses that contribute to the disease.  Measurement of RBP levels has also been useful in detection and characterization of diseases including hypertension and certain cancers, among other conditions.