Journal List > J Korean Soc Endocrinol > v.20(5) > 1063816

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Kim, Cho, Park, Lee, Oh, Jeong, Hong, Ihm, Kim, Yu, Choi, Yoo, Park, Kim, and Rho: Duration of Preparation for Postoperative Radioiodine Administration in Differentiated Thyroid Carcinoma
Original Article
Journal of Korean Society of Endocrinology

Journal of Korean Society of Endocrinology 2005; 20(5): 460-466.

Published online: 20 October 2005

DOI: https://doi.org/10.3803/jkes.2005.20.5.460

Duration of Preparation for Postoperative Radioiodine Administration in Differentiated Thyroid Carcinoma

Hyeon Kyu Kim, Min Ho Cho, Choel Young Park, Seong Jin Lee, Gi Weon Oh, In Kyung Jeong, Eun Gyung Hong, Sung Hee Ihm, Doo-Man Kim, Jae Myung Yu, Moon Gi Choi, Hyung Joon Yoo, Sung Woo Park, Jin Hwan Kim1, Young Soo Rho1

Department of Internal Medicine, College of Medicine, Hallym University, Chuncheon, Korea.

1Department of Otorhinolaryngology-Head and Neck Surgery, College of Medicine, Hallym University, Chuncheon, Korea.

Received 8 September 2005       Accepted 20 September 2005

Copyright © 2005 Korean Endocrine Society

Abstract

Background

Radioiodine treatment is effective for the removal of remnant thyroid tissues after thyroidectomy in patients with differentiated thyroid carcinoma. To induce the elevation of serum TSH level which facilitates the uptake of radioiodine into remnants, a 4 to 6 week interval between thyroidectomy and radioiodine administration has been established. During the period of preparation, most patients have experienced overt symptoms of hypothyroidism which have led to the development of alternative strategies. Some reports have suggested that the interval could be reduced to about 3 weeks with less symptoms. We reevaluated the adequate time needed for the elevation of serum TSH level above 30 µU/mL after thyroidectomy.

Methods

Forty five patients who had undergone total thyroidectomy for differentiated thyroid carcinoma were investigated. Serum TSH and free T4 levels were measured one or more times within 3 weeks after operation (total 97 blood samples). Eighty nine blood samples were obtained within 15 days.

Results

In 41 patients (91.1%) serum TSH levels increased to 30 µU/mL until 15 days after operation. Until postoperative 21 days, serum TSH levels in all the other patients reached 30 µU/mL. In linear equation, the daily increment of serum TSH levels was 2.62 µU/mL for the first 8 days after operation and 5.34 µU/mL for the next 7 days. The half-life of serum free T4 levels showed marked individual variations.

Conclusion

Measurement of serum TSH level at about 15 days after total thyroidectomy for differentiated thyroid carcinoma may be useful in determining the time of radioiodine administration.

Keywords: Thyroid cancer, Thyrotropin, Thyroidectomy

Figures and Tables

Fig. 1
Changes in serum TSH (A) and free T4 (B) levels after thyroidectomy. Levels at the 1st (or 2nd) week were measured from the 5th through the 7th day after operation in 31 patients (or from the 13th through the 15th day after operation in 32 patients).
jkse-20-460-g001
Fig. 2
Linear regression of serum TSH levels on days after thyroidectomy. The equations are y=2.62χ+1.06 (r2=0.507) for line A, y=5.34χ-11.36 (r2=0.187) for line B, and y=4.46χ-2.69 (r2=0.694) for line C.
jkse-20-460-g002
Fig. 3
Non-linear regression of serum TSH levels on days after thyroidectomy. The equation of the best-fit curve (solid line) is y=1.575+1.585χ-0.003χ2+0.033χ3-0.001χ4 (R2=0.740). The dotted lines represent the upper and lower limits of 95% prediction interval.
jkse-20-460-g003
Table 1
Characteristics of 45 Patients
jkse-20-460-i001

Data are means ± SD.

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