Use of Normalized Serum Thyroxine (T4N)

The measurement of serum thyroxine is an indicator of the total hormone present in the serum; it is directly dependent on the protein bound portion of thyroxine. This portion is altered by various physiological states, sex hormone uses, and pregnancy, so that thyroxine determinations under these conditions may be unreliable. The dual competitive protein binding analysis reintroduces the patient's serum into the test system, a procedure which provides additional competitive binding sites that have a corrective effect on serum thyroxine values altered by physiological conditions but will not be affected by abnormal or pathological thyroid functional states. Clinical data and thyroid function tests in normal subjects and hyperthyroid and hypothyroid patients, pregnant women, and women receiving estrogens revealed that the normalized tetraiodothyronine (T4N) determinations correlated better with the patient's thyroid status than did earlier thyroid function tests.