Retinol-Binding Protein (RBP)

Quantitative determination of Retinol-Binding Protein (RBP) levels in serum and plasma using turbidimetric technology

Gentian Retinol-Binding Protein (RBP) Immunoassay

The Gentian Retinol-Binding Protein Immunoassay is a quantitative immunoassay for detection of Retinol-Binding Protein (RBP or RBP4) in human serum and plasma. RBP is a transport protein for retinol (derivate of vitamin A) in blood. RBP is synthesised and stored in the liver before binding to one retinol and one prealbumin (transthyretin (TTR)) to stabilise the complex and avoid renal filtration. Retinol-free RBP in the circulation is filtrated by the kidney and almost completely reabsorbed by the proximal renal tubule.^1-4 The concentration of RBP in blood remains mostly constant in healthy individuals, though the levels can be altered in many conditions and disorders such as vitamin A deficiency, undernutrition, diabetes and renal dysfunction.

Gentian Retinol-Binding Protein Immunoassay is a turbidimetric assay that is rapidly performed in only 10 minutes. The assay is instrument independent and can be applied on a wide range of automated clinical chemistry analysers. It is CE-marked, UKCA-marked and FDA Exempt.

RBP and vitamin A

Main storage site of vitamin A is the liver. For mobilisation, the vitamin A derivative retinol is bound to the carrier protein RBP, secreted into blood and transported throughout the body. In cases of vitamin A deficiency, the liver will not store sufficient amounts of vitamin A to ensure the constant level of the RBP-retinol complex in blood. Vitamin A deficiency (VAD) is therefore reflected by reduced levels of the surrogate marker RBP, making the assay useful in the assessment of vitamin A status.^{3, 5}

RBP and undernutrition

RBP is a low molecular weight protein and therefore responds to both protein and calorie restriction and can reflect the individual’s protein- and nutritional status. Studies have shown an inverse association between RBP levels and the severity of malnutrition and RBP can therefore be used as an aid in determining undernutrition.^6-8

RBP and diabetes

An association between RBP and insulin resistance and diabetes has been identified.² In type 2 diabetes (T2D) and gestational diabetes RBP levels are elevated, correlated with the magnitude of insulin resistance and is associated with several comorbidities of T2D.^9-12 Measurements of serum RBP can therefore serve as a non-invasive and accessible method for assessing the risk of diabetes.

RBP and renal dysfunction

RBP is filtered in the glomerulus of the kidney, reabsorbed, and catabolised by the proximal tubules.² In patients with reduced glomerular filtration rate (GFR) the levels of RBP will accumulate in blood.^13,14 Hence, an increase in serum and plasma levels of RBP may reflect renal dysfunction.^15,16

Retinol-Binding Protein - RBP validation kit

Technical details

Assay Performance
Sample type	Fresh plasma and serum
Assay type	Turbidimetric assay
Format	Liquid reagents, ready to use
Precision (sample >1 mg/L)*	Total CV <5%
LoQ*	7.81 mg/L*
Security zone*	Up to 600 mg/L
Measuring range**	7.8-139 mg/L

* Instrument specific ** Lot- and instrument specific
The method has been standardised with a benchmark method traceable to the international standard.

For more details on Retinol-Binding Protein (RBP) products and prices please contact us at marketing@gentian.com

Gentian Retinol-Binding Protein Immunoassay is an instrument-independent turbidimetric assay. Our instrument validation team can assist with establishing applications on clinical chemistry instruments of interest. The assay is CE-marked and FDA 510(k) Exempt.

For more details on Retinol-Binding Protein (RBP) products and prices please contact us at marketing@gentian.com

Product no.	Product	Content
11001	Gentian Retinol-Binding Protein Reagent Kit	R1: 40 mL R2: 13 mL
11020	Gentian Retinol-Binding Protein Control Low	2 mL
11021	Gentian Retinol-Binding Protein Control Medium	2 mL
11022	Gentian Retinol-Binding Protein Control High	2 mL
11051	Gentian Retinol-Binding Protein Calibrator Kit	5 x 1 mL

For more details on Retinol-Binding Protein (RBP) products and prices please contact us at marketing@gentian.com

Turbidimetric test

Faster throughput

Open channel

10 minutes to result

Cost efficient

Contact us for further information

Explore RBP in your laboratory - fill out the form or send an email to marketing@gentian.com for more information about the product and prices.

Frequently asked questions

What is the assay principle for Retinol-Binding Protein (RBP)?

The Gentian RBP Immunoassay is a Turbidimetric Immunoassay (TIA) on multiple platforms for in vitro diagnostic testing of RBP in human plasma and serum samples.

Is Gentian Retinol-Binding Protein (RBP) an open channel turbidimetric assay?

Retinol-Binding Protein (RBP) is an open channel assay, meaning it can be added to all clinical chemistry analysers. Diagnostic laboratories are thereby not limited to the use of one specific instrument offering Retinol-Binding Protein (RBP) but can apply the assay on their available instrumentation and thereby fill the open menu gaps.

Our instrument validation team can assist with establishing applications on clinical chemistry analysers of interest.

Which clinical chemistry analysers can Retinol-Binding Protein (RBP) be applied on?

Retinol-Binding Protein (RBP) can be applied on a wide range of clinical chemistry analysers.

What is retinol?

Vitamin A is an essential nutrient and a fat-soluble vitamin. The term umbrellas a group of unsaturated organic compounds, which include retinol, retinal, and retinoic acid. Retinol is the alcohol derivate of vitamin A transported from the liver to tissues by RBP.³

What is RBP?

RBP (also called RBP4) is a single polypeptide chain protein with molecular mass of around 21 kDa and a member of the lipocalin family. It is the only known specific transport protein for retinol (vitamin A).⁴

What is apo-RBP?

Free RBP not bound to retinol is called apo-RBP. Apo-RBP is subjected to renal filtration and the ration of the apo-RBP form in plasma is normally of only around 15%.³

What is holo-RBP?

RBP bound to retinol (in a 1:1 complex) is called holo-RBP. In the circulation RBP is mostly saturated with retinol, around 85%.³

What is prealbumin?

Prealbumin, also known as transthyretin (TTR), is a tetrameric protein of around 55 kDa. Prealbumin binds to apo-RBP in the liver and forms a 1:1:1 complex (retinol:RBP:TTR) increasing its molecular weight, thereby preventing renal filtration and extending RBP’s serum half-life.⁴

What is STRA6?

Stimulated by retinoic acid 6 (STRA6) is a membrane receptor transporting retinol provided by RBP across the cell membrane of extrahepatic tissues. Together with homologues receptor ‘stimulated by retinoic acid 6-like’ (STRA6L) it is the only receptor known for active membrane transport of retinol.⁴

References:

Kanai M et al. Retinol-binding protein: the transport protein for vitamin A in human plasma. J Clin Invest, 1968
Steinhoff JS et al. Retinoid Homeostasis and Beyond: How Retinol Binding Protein 4 Contributes to Health and Disease. Nutrients, 2022
Tanumihardjo SA et al. Biomarkers of Nutrition for Development (BOND)-Vitamin A Review. J Nutr, 2016
Steinhoff JS et al. Biological Functions of RBP4 and Its Relevance for Human Diseases. Front Physiol, 2021
de Pee S et al. Biochemical indicators of vitamin A deficiency: serum retinol and serum retinol binding protein. J Nutr, 2002
Sergi G et al. Role of visceral proteins in detecting malnutrition in the elderly. Eur J Clin Nutr, 2006
Smith FR et al. Plasma vitamin A, retinol-binding protein and prealbumin concentrations in protein-calorie malnutrition. III. Response to varying dietary treatments. Am J Clin Nutr, 1975
Pisprasert V et al. Moderately high-protein enteral formula improved retinol-binding protein in tube-fed patients: A multicentre open study. Nutr Health, 2017
Nono Nankam PA et al. Retinol-binding protein 4 in obesity and metabolic dysfunctions. Mol Cell Endocrinol, 2021
Mousavi SN et al. Association of Leptin and Retinol Binding Protein 4 with the Risk of Gestational Diabetes: A Systematic Review and Meta-Analysis of Observational Studies. Indian J Endocrinol Metab, 2023
Flores-Cortez YA et al. Interplay of retinol binding protein 4 with obesity and associated chronic alterations (Review). Mol Med Rep, 2022
Olsen T et al. Retinol, Retinoic Acid, and Retinol-Binding Protein 4 are Differentially Associated with Cardiovascular Disease, Type 2 Diabetes, and Obesity: An Overview of Human Studies. Adv Nutr, 2020
Zhang WX et al. Decreased retinol-binding protein 4 in the sera of patients with end-stage renal disease after kidney transplantation. Genet Mol Res, 2014
Xun C et al. Circulating RBP4 Increase and Its Diagnosis of Chronic Kidney Disease. Ann Clin Lab Sci, 2018
Zhang L et al. The Role of Circulating RBP4 in the Type 2 Diabetes Patients with Kidney Diseases: A Systematic Review and Meta-Analysis. Dis Markers, 2020
Ye Z et al. Correlation and Diagnostic Value of Serum Cys-C, RBP4, and NGAL with the Condition of Patients with Traumatic Acute Kidney Injury. Evid Based Complement Alternat Med, 2021

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