Which test is not used to assess vitamin A status?

Which test is not used to assess vitamin A status?

• A. Plasma carotenoid level
• B. Serum retinol concentration
• C. Plasma transthyretin-retinol binding protein (TTR-RBP) concentration
• D. Serum retinol binding protein level

Answer: (A)

Vitamin A status is evaluated using markers tied to retinol and its transport system. Plasma carotenoid level does not directly reflect vitamin A stores or availability because carotenoids are precursors whose circulating levels depend largely on intake, absorption, and conversion efficiency, not on liver retinol stores. In contrast, serum retinol concentration is a traditional indicator of vitamin A status (though it can stay normal until stores are depleted), and serum retinol-binding protein, often in conjunction with transthyretin, serves as a related measure of retinol transport. These markers can be influenced by inflammation or protein status, but they still provide information about vitamin A status. Thus, plasma carotenoid level is not used to assess vitamin A status.

Vitamin A status is evaluated using markers tied to retinol and its transport system. Plasma carotenoid level does not directly reflect vitamin A stores or availability because carotenoids are precursors whose circulating levels depend largely on intake, absorption, and conversion efficiency, not on liver retinol stores. In contrast, serum retinol concentration is a traditional indicator of vitamin A status (though it can stay normal until stores are depleted), and serum retinol-binding protein, often in conjunction with transthyretin, serves as a related measure of retinol transport. These markers can be influenced by inflammation or protein status, but they still provide information about vitamin A status. Thus, plasma carotenoid level is not used to assess vitamin A status.