Major thyroxine binding protein ?
**Core Concept**
Thyroid hormone transport in the blood is crucial for maintaining normal thyroid function and preventing toxicity. The major thyroxine-binding protein is responsible for binding and transporting thyroxine (T4) and triiodothyronine (T3) in the bloodstream.
**Why the Correct Answer is Right**
The major thyroxine-binding protein is Transthyretin (TTR), also known as Prealbumin. It is a transport protein that primarily binds T4 and T3, facilitating their transport from the thyroid gland to peripheral tissues. Transthyretin also binds vitamin A, which is another important transport function. The binding of T4 and T3 to Transthyretin is crucial for maintaining the balance of thyroid hormones in the body.
**Why Each Wrong Option is Incorrect**
**Option A:** Albumin is a major binding protein for various substances, including bilirubin, fatty acids, and calcium, but it is not the primary thyroxine-binding protein.
**Option B:** Hemopexin is a plasma protein that binds heme, but it is not involved in thyroid hormone transport.
**Option C:** Ceruloplasmin is a copper-transporting protein, but it is not a major binding protein for thyroxine.
**Clinical Pearl / High-Yield Fact**
Transthyretin (Prealbumin) levels can be used as a marker of nutritional status and acute phase response, as well as a predictor of mortality in critically ill patients.
**Correct Answer: C. Transthyretin (Prealbumin)**