TSH-suppressive doses of levothyroxine are required to achieve preoperative native serum triiodothyronine levels in patients who have undergone total thyroidectomy.
OBJECTIVE
Thyroidal production of triiodothyronine (T(3)) is absent in patients who have undergone total thyroidectomy. Therefore, relative T(3) deficiency may occur during postoperative levothyroxine (L-T(4)) therapy. The objective of this study was to evaluate how the individual serum T(3) level changes between preoperative native thyroid function and postoperative L-T(4) therapy.


METHODS
We retrospectively studied 135 consecutive patients with papillary thyroid carcinoma, who underwent total thyroidectomy. Serum free T(4) (FT(4)), free T(3) (FT(3)), and TSH levels measured preoperatively were compared with those levels measured on postoperative L-T(4) therapy.


RESULTS
serum tsh levels during postoperative L-T(4) therapy were significantly decreased compared with native TSH levels (P<0.001). serum FT(4) levels were significantly increased (P<0.001). Serum FT(3) levels were significantly decreased (P=0.029). We divided the patients into four groups according to postoperative serum TSH levels: strongly suppressed (less than one-tenth of the lower limit); moderately suppressed (between one-tenth of the lower limit and the lower limit); normal limit; and more than upper limit. Patients with strongly suppressed TSH levels had serum FT(3) levels significantly higher than the native levels (P<0.001). Patients with moderately suppressed TSH levels had serum FT(3) levels equivalent to the native levels (P=0.51), and patients with normal TSH levels had significantly lower serum FT(3) levels (P<0.001).


CONCLUSIONS
Serum FT(3) levels during postoperative L-T(4) therapy were equivalent to the preoperative levels in patients with moderately suppressed TSH levels. Our study indicated that a moderately TSH-suppressive dose of L-T(4) is required to achieve the preoperative native serum T(3) levels in postoperative L-T(4) therapy.
Center for Excellence in Thyroid Care, Kuma Hospital, 8-2-35, Shimoyamate-Dori, Chuo-Ku, Kobe-City, Hyogo 650-0011, Japan. ito02@kuma-h.or.jp
Mitsuru
M
Ito
Akira
A
Miyauchi
Shinji
S
Morita
Takumi
T
Kudo
Eijun
E
Nishihara
Minoru
M
Kihara
Yuuki
Y
Takamura
Yasuhiro
Y
Ito
Kaoru
K
Kobayashi
Akihiro
A
Miya
Sumihisa
S
Kubota
Nobuyuki
N
Amino
D000328:Adult; D000368:Aged; D002277:Carcinoma; D002291:Carcinoma, Papillary; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011300:Preoperative Care / Q000379:methods*; D012189:Retrospective Studies; D000077273:Thyroid Cancer, Papillary; D013964:Thyroid Neoplasms / Q000097:blood* / Q000188:drug therapy / Q000601:surgery; D013965:Thyroidectomy / Q000009:adverse effects*; D013972:Thyrotropin / Q000037:antagonists & inhibitors / Q000097:blood*; D013974:Thyroxine / Q000008:administration & dosage*; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine