Preparation for radioactive iodine administration in differentiated thyroid cancer patients.
OBJECTIVE
Because in recent years the practice of TSH suppression has changed, and thyroxine doses have been reduced significantly in the treatment of patients with low-risk differentiated thyroid cancer, the goal of this study was to determine the time needed to attain a target TSH level (of 30 mIU/l) following levothyroxine withdrawal in patients treated with thyroxine according to current guidelines, in anticipation of radioactive iodine (RAI) administration.


METHODS
Observational study.


METHODS
Thirteen consecutive patients with differentiated thyroid cancer on suppressive doses of levothyroxine planned for RAI administration. Five of the patients received cholestyramine in an attempt to facilitate TSH recovery.


METHODS
Serum TSH, free-T3 and free-T4, at 3-4-day intervals.


RESULTS
In 13 patients on suppressive doses of thyroxine, on 15 separate occasions, baseline TSH levels were between 0.01 and 0.4 mIU/l. The mean interval required to reach the target TSH concentration of at least 30 mIU/l was 17 days (95% CI 15-19; range 11-28 days). Cholestyramine had no effect on the rate of TSH recovery. Once TSH concentration became detectable, it increased exponentially; and once it reached the upper limit of normal, it rarely took more than 10 days to attain target level.


CONCLUSIONS
Attaining target TSH level before radioactive iodine administration requires a considerably shorter time than is currently recommended. Reducing preparation time might improve patients' acceptance of the procedure.
D000328:Adult; D000368:Aged; D002454:Cell Differentiation; D002792:Cholestyramine Resin / Q000627:therapeutic use; D005260:Female; D006207:Half-Life; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D013964:Thyroid Neoplasms / Q000097:blood* / Q000188:drug therapy / Q000532:radiotherapy*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood / Q000627:therapeutic use; D014284:Triiodothyronine / Q000097:blood
D007457:Iodine Radioisotopes; D014284:Triiodothyronine; D002792:Cholestyramine Resin; D013972:Thyrotropin; D013974:Thyroxine