Prealbumin serves as a transport protein for which hormone or molecule?

• A. Transthyretin/TBPA for T4
• B. Retinol Binding Protein for Vitamin A
• C. Albumin for bilirubin
• D. Transferrin for iron

Answer: (A)

Prealbumin, also known as transthyretin, is a transport protein whose main role is to carry thyroid hormone in the blood. It binds thyroxine (T4) and helps shuttle it to tissues. It also forms a complex with retinol-binding protein to assist in vitamin A transport, but its primary transport function tied to its name and function is thyroxine. In contrast, iron is carried mainly by transferrin, and bilirubin is carried by albumin, so those are not the primary roles of prealbumin.