Do We Really Need to Do Both fT4 and TSH in Evaluating Patients?

Question

Dear Sir, Sincere admiration for your great website. Regarding evaluation of thyroxine replacement therapy, it is always suggested to evaluate TSH and free T4. However except in the situation of pregnancy (where only depending on TSH could result in a retarded action), I don' t see much reason to determine both values. Is it wrong to check only TSH ?

Dr. Henri Maex, Antwerp, Belgium