Retinol Binding Protein (RBP) ELISA Kit

Sample

serum, plasma, dried blood spot, urine

Species Reactivity

Human

Intended Use

The Retinol Binding Protein (RBP) kit is designed to quantitatively measure RBP present in serum, plasma, dried blood spot (DBS) and urine samples. Please read the complete kit insert before performing this assay.

Storage

All components of this kit should be stored at 4°C until the expiration date of the kit.

Precision

Intra Assay Precision - 10 μL Format
Three human serum and plasma samples were diluted with Assay Buffer and run in replicates of 20 in an assay. The mean and precision of the calculated RBP concentrations were:

Inter Assay Precision - 10 μL Format
Three human serum and plasma samples were diluted with Assay Buffer and run in duplicates in twenty-three assays run over multiple days by four operators. The mean and precision of the calculated RBP concentrations were:

Inter Assay Precision - 100 μL Format
Three human serum and plasma samples were diluted with Assay Buffer and run in duplicates in ten assays run over multiple days by four operators. The mean and precision of the calculated RBP concentrations were:

Detection Limit

The Limit of Detection for the 10 μL and the 100 μL sample format was determined in a similar manner by comparing the OD's for twenty runs for each of the zero standard and a low concentration human sample in the appropriate volume standard curve.
Limit of Detection was determined as 8.09 ng/mL for 10 μL and 0.995 ng/mL for 100 μL sample size.

Sensitivity

Sensitivity with the 10 μL and the 100 μL sample volume was calculated by comparing the OD's for twenty wells run for each of the B0 and standard #8. The detection limit was determined at two (2) standard deviations from the B0 along the appropriate volume standard curve.
Sensitivity was determined as 5.69 ng/mL for 10 μL and 1.36 ng/mL for 100 μL sample size.

General Description

Retinol binding protein (RBP) is from a family of structurally related proteins that bind small hydrophobic molecules such as bile pigments, steroids, odorants, etc1 . 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 (vitamin A).
RBP binds retinol in a 1:1 stoichiometry, which serves to not only solubilize retinol but also protect it from oxidation. When in serum, the majority of RBP bound with retinol is reversibly complexed with transthyretin (prealbumin)2,3. This complex then transports retinol to specific receptors of various tissues in the body. Vitamin A status is reflected by serum concentration as it is hemostatically controlled and does not fall until stores are dramatically reduced4,5.
RBP has been shown to be a useful surrogate marker for retinol because of the approximate 1:1 (molar) correlation between retinol and RBP in serum1, 6,7, which implies that RBP may be used to assess and monitor vitamin A deficiency (VAD) in populations. The World Health Organization has estimated that 250 million children have moderate to severe VAD7 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.
RBP has also been shown to be a useful marker for renal function8 as it is totally filtered by the glomeruli and reabsorbed by proximal tubules9 . This has made the measurement of urinary RBP a tool to study renal function in heart10 or kidney11 transplant recipients.