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Effects of Thyroid Hormone Withdrawal and Recombinant Human Thyrotropin on Glomerular Filtration Rate During Radioiodine Therapy for Well-Differentiated Thyroid Cancer.

BACKGROUND
Renal function is related to thyroid hormonal status, and glomerular filtration rate (GFR) seems to be impaired in patients with hypothyroidism. The aim of this work was to evaluate quantitatively the effect of hypothyroidism on GFR using a (51)Cr-EDTA radioisotope assay.


METHODS
Twenty-eight patients without known renal disease or dysfunction who had been referred for radioiodine therapy (RIT) after total thyroidectomy were enrolled in this study and divided into two groups. Group A underwent thyroid hormone withdrawal (THW) resulting in hypothyroidism, while group B underwent recombinant human thyrotropin (rhTSH) stimulation and hence remained euthyroid. GFR was assessed by (51)Cr-EDTA before and after THW or rhTSH.


RESULTS
No clinical differences were observed between the two groups. The mean ± SD GFRs were 94 ± 19 mL/min/1.73 m(2) before THW and 76 ± 16 mL/min/1.73 m(2) after THW for group A (p = 0.009), and 91 ± 18 mL/min/1.73 m(2) before rhTSH and 93 ± 15 mL/min/1.73 m(2) after rhTSH for group B (p = 0.613). The percent decrease in GFR during hypothyroidism is approximately 18-22%.


CONCLUSION
GFR decreases in patients with normal kidney function during THW for RIT, and rhTSH preserves GFR in these patients. This GFR impairment following thyroidectomy is related to hypothyroidism due to a significant reduction in thyroid hormone levels and is not due to a rise in the TSH level.