This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Major thyroxine binding protein ? 
Select and explain. 
A. Albumin, B. Prealbumin, C. Globulin, D. Transferrin
C: Globulin
Answer: C: Globulin 
Explanation: Ans. is 'c' i.e., GlobulinMost of the circulating thyroid, hormones are protein bound, leaving only 0.02% T4 and about 0.2% T3 unbound or free.There are three hormone binding plasma proteins, i.e., thyroxine binding globulin (major thyroid hormone binding protein), thyroxine binding albumin and thyroxine binding prealbumin.Thyroid binding globulin level is raised in pregnancy and by drugs estrogens, methadone, heroin, tranquilizers, clofibrate.TBG decreases by glucocoicoid, androgen, danazol, asparginase (cancer chemotherapy) and nephrotic syndrome.