J Korean Soc Endocrinol.  2005 Oct;20(5):460-466. 10.3803/jkes.2005.20.5.460.

Duration of Preparation for Postoperative Radioiodine Administration in Differentiated Thyroid Carcinoma

• Kim HK
• Cho MH
• Park CY
• Lee SJ
• Oh GW
• Jeong IK
• Hong EG
• Ihm SH
• Kim DM
• Yu JM
• Choi MG
• Yoo HJ
• Park SW
• Kim JH
• Rho YS

• KMID: 2200593
• DOI: http://doi.org/10.3803/jkes.2005.20.5.460

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 30microU/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 microU/mL until 15 days after operation. Until postoperative 21 days, serum TSH levels in all the other patients reached 30microU/mL. In linear equation, the daily increment of serum TSH levels was 2.62microU/mL for the first 8 days after operation and 5.34micorU/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.

MeSH Terms

Half-Life
Humans
Hypothyroidism
Thyroid Gland*
Thyroid Neoplasms*
Thyroidectomy
Thyrotropin
Thyrotropin

Figure

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  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).

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  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.

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  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.

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