The high prevalence of reversible subclinical hypothyroidism with elevated serum thyroglobulin levels in chronic kidney disease patients
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Background: We examined the thyroid function of non-dialysis-dependent chronic kidney disease (CKD) patients in Japan. Methods: Serum-free thyroxine, free triiodothyronine, thyroid-stimulating hormone (TSH), and thyroglobulin (Tg) levels were evaluated in 37 CKD patients. CKD was defined as sustained kidney damage for more than 3 months and was classified as CKD 1+2 (n = 11), 3+4 (n = 10), or 5 (n = 16), which were defined by glomerular filtration rates of = 60, 15 - 59, or < 15 mL/min/1.73 m(2), respectively. Results: The prevalence of primary hypothyroidism (TSH = 4.83 mU/L) in CKD 1+2, CKD 3+4, and CKD 5 was 9%, 20%, and 56%, respectively (p < 0.05). Unexpectedly, elevated serum Tg levels (> 30 ng/mL), a marker of the reversible recovery of the thyroid function, were found in 67% of the CKD 5 patients (p < 0.05). The serum TSH and Tg levels became lower, without replacement therapy, after the initiation of hemodialysis and iodine restriction, and there was a significant correlation between the serum TSH and Tg levels in the CKD 5 patients (p < 0.05). Conclusion: The high prevalence of reversible hypothyroidism and the TSH-dependent elevation of the serum Tg levels was suggested in Japanese patients with advanced CKD. The excess ingestion and the impaired urinary excretion of iodine may be responsible for this reversible thyroid dysfunction.