Which biomarker is used as an alternative marker to assess vitamin A status aside from serum retinol?

• A. Elevated liver enzymes
• B. Retinol-binding Protein (RBP) measurement
• C. Ferritin levels
• D. Urinary retinol excretion

Answer: (B)

Vitamin A status is often tracked with serum retinol, but this measure can stay normal until liver stores are quite depleted. Retinol-binding Protein (RBP) measurement provides a practical alternative because vitamin A travels in the blood bound to RBP. The amount of holo-RBP reflects available retinol and, to some extent, hepatic vitamin A stores, making RBP a more sensitive surrogate indicator of overall vitamin A status in many situations. Immunoassays for RBP are commonly used and are typically more accessible and cost-effective than direct retinol measurements.

Be mindful that RBP levels can be influenced by protein status and inflammation, so results are interpreted in context (often alongside inflammatory markers). Other options listed, like elevated liver enzymes or ferritin, relate to liver injury or iron stores, not vitamin A status, and urinary retinol excretion is not a standard marker for assessing vitamin A status.