What may be used other than serum retinol concentration for assessing vitamin A status?

What may be used other than serum retinol concentration for assessing vitamin A status?

• A. Measurement of retinol-binding protein (RBP) and transthyretin-retinol binding protein (TTR-RBP)
• B. Plasma carotenoids
• C. Serum ferritin
• D. Urinary retinol

Answer: (A)

Vitamin A status is better reflected by transport proteins in the blood than by serum retinol alone, because retinol levels stay fairly constant until liver stores are severely depleted. The retinol-binding protein (RBP) carries retinol from the liver to tissues, so measuring RBP gives a more sensitive sense of vitamin A status. When vitamin A stores are adequate, RBP in the blood is higher; as stores decline, RBP production falls and circulating retinol transport diminishes sooner than serum retinol does. Using the transthyretin-RBP complex adds stability in the circulation and reduces variability from protein status, so assessing this complex (or the RBP measurement in the context of transthyretin/prealbumin) provides a more accurate assessment across different nutritional states. Some approaches also use the RBP to transthyretin ratio to account for inflammation or acute-phase changes that can independently affect these proteins. Be mindful that RBP-based measures can still be influenced by protein-energy status, zinc status, and inflammation, so interpreting results alongside inflammatory markers (like CRP) and overall nutrition status improves accuracy. By contrast, plasma carotenoids mainly reflect intake and bioavailability, not liver stores; serum ferritin relates to iron stores and inflammation rather than vitamin A; urinary retinol is not a valid method for assessing vitamin A status.

Vitamin A status is better reflected by transport proteins in the blood than by serum retinol alone, because retinol levels stay fairly constant until liver stores are severely depleted. The retinol-binding protein (RBP) carries retinol from the liver to tissues, so measuring RBP gives a more sensitive sense of vitamin A status. When vitamin A stores are adequate, RBP in the blood is higher; as stores decline, RBP production falls and circulating retinol transport diminishes sooner than serum retinol does.

Using the transthyretin-RBP complex adds stability in the circulation and reduces variability from protein status, so assessing this complex (or the RBP measurement in the context of transthyretin/prealbumin) provides a more accurate assessment across different nutritional states. Some approaches also use the RBP to transthyretin ratio to account for inflammation or acute-phase changes that can independently affect these proteins.

Be mindful that RBP-based measures can still be influenced by protein-energy status, zinc status, and inflammation, so interpreting results alongside inflammatory markers (like CRP) and overall nutrition status improves accuracy.

By contrast, plasma carotenoids mainly reflect intake and bioavailability, not liver stores; serum ferritin relates to iron stores and inflammation rather than vitamin A; urinary retinol is not a valid method for assessing vitamin A status.