Only a part, ranging from 15% to 20%, of active T3 is produced by thyroid; the rest derives from T4 peripheral conversion; so, the treatments implying T3 plus T4 administration are necessarily better than T4 administration alone. In order to deeply study the problem, 50 patients undergoing thyroidectomy were examined: 33 affected by benign forms and 17 affected by cancers. TSH, T4 and T3 levels were measured immediately before surgery and after 2 and 4 months. T4 doses were adjusted to obtained normal TSH levels in patients affected by benign forms, while researchers tried to reach values slightly lower than the minimal threshold in patients affected by cancer. There was no significant difference in T3 values: after thyroidectomy, T3 levels were lower only in 7 patients presenting TSH > 4.5 mU/l compared with patients with normal or suppressed TSH.
