Vitamin A (Retinol).

What does this test assess?

This method quantifies retinol (vitamin A) from a single dried blood spot, supporting the detection of both deficiency and excess states. Retinol status has direct implications for vision, immune function, reproduction, and embryonic development.

Clinical indications include:

• Detection and monitoring of vitamin A deficiency (VAD), the leading cause of preventable childhood blindness worldwide
• Identification of hypervitaminosis A, associated with hepatotoxicity, teratogenicity, and skeletal abnormalities
• Prenatal and antenatal monitoring of retinol status
• Assessment in malabsorption syndromes (coeliac disease, cystic fibrosis, short bowel syndrome)
• Monitoring supplementation programmes in public health and clinical nutrition
• Evaluation in chronic liver disease, where retinol metabolism is impaired

About Vitamin A

Vitamin A is a fat-soluble essential nutrient that exists in two principal dietary forms: preformed retinol (from animal sources) and provitamin A carotenoids such as β-carotene (from plant sources). In the body, retinol is the predominant circulating form and serves as the primary biomarker for vitamin A status.

Retinol is essential for the visual cycle, where it is converted to 11-cis-retinal in photoreceptor cells. Beyond vision, it plays critical roles in immune cell differentiation, epithelial barrier integrity, and embryonic morphogenesis through its active metabolite, retinoic acid.

Deficiency is particularly prevalent in low- and middle-income countries and among populations with restricted dietary diversity. In high-income settings, deficiency is more commonly associated with malabsorption disorders, chronic liver disease, or restrictive diets. Conversely, excessive supplementation can lead to acute or chronic toxicity, making accurate quantification important for both deficiency screening and safety monitoring.

Retinol circulates bound to retinol-binding protein (RBP), and its serum concentration is homeostatically regulated until liver stores are significantly depleted. This means that circulating retinol may remain normal until deficiency is advanced, underscoring the value of precise analytical measurement.

Analytical technique

Retinol is extracted from a dried blood spot and quantified using isotope-dilution LC-MS/MS. The method employs a deuterium-labelled internal standard (retinol-d5) to correct for matrix effects and extraction variability, ensuring accurate and reproducible results.

LC-MS/MS provides superior specificity compared to traditional HPLC-UV methods, eliminating interference from carotenoids and other retinoid metabolites that can confound UV-based detection.

Literature

1. WHO. “Global prevalence of vitamin A deficiency in populations at risk 1995–2005.” WHO Global Database on Vitamin A Deficiency, 2009.
2. Tanumihardjo SA. “Vitamin A: biomarkers of nutrition for development.” American Journal of Clinical Nutrition, 2011, 94(2):658S–665S. 10.3945/ajcn.110.005777
3. Wiseman EM, Bar-El Dadon S, Reifen R. “The vicious cycle of vitamin A deficiency: a review.” Critical Reviews in Food Science and Nutrition, 2017, 57(17):3703–3714. 10.1080/10408398.2016.1160362
4. Sapin V et al. “Vitamin A and pregnancy: a narrative review.” Nutrients, 2015, 7(3):1400–1423. 10.3390/nu7031400
5. Zhong G et al. “Determination of retinol and α-tocopherol in dried blood spots by LC-MS/MS.” Journal of Chromatography B, 2020, 1159:122363. 10.1016/j.jchromb.2020.122363