title: Risk factors for developing hyponatremia in thyroid cancer patients undergoing radioactive iodine therapy.
abstract: BACKGROUND
  Due to the alarming increase in the incidence of thyroid cancer worldwide, more patients are receiving postoperative radioactive iodine (RAI) therapy and these patients are given a low-iodine diet along with levothyroxine withdrawal to induce a hypothyroid state to maximize the uptake of RAI by thyroid tissues. Recently, the reported cases of patients suffering from life-threatening severe hyponatremia following postoperative RAI therapy have increased. This study aimed to systematically assess risk factors for developing hyponatremia following RAI therapy in post-thyroidectomy patients.
  
  
  METHODS
  We reviewed the medical records of all thyroid cancer patients who underwent thyroidectomy and postoperative RAI therapy from July 2009 to February 2012. Demographic and biochemical parameters including serum sodium and thyroid function tests were assessed along with medication history.
  
  
  RESULTS
  A total of 2229 patients (47.0±11.0 years, female 76.3%) were enrolled in the analysis. Three hundred seven patients (13.8%) of all patients developed hyponatremia; 44 patients (2.0%) developed moderate to severe hyponatremia (serum Na+≤130 mEq/L) and another 263 (11.8%) patients showed mild hyponatremia (130 mEq/L<serum Na+≤135 mEq/L). In univariate analysis, old age, female sex, presence of hypertension, presence of diabetes, use of thiazide diuretics, use of angiotensin receptor blocker or angiotensin-converting enzyme inhibitors, lung metastasis, and hyponatremia and lower estimated glomerular filtration rate at the start of RAI therapy were significantly associated with hyponatremia in patients undergoing RAI therapy after total thyroidectomy. Multivariate analysis showed that old age, female sex, use of thiazide diuretics, and hyponatremia at the initiation of RAI therapy were independent risk factors for the development of hyponatremia.
  
  
  CONCLUSIONS
  Our data suggest that age greater than 60 years, female sex, use of thiazide, and hyponatremia at the initiation of RAI therapy are important risk factors for developing hyponatremia following RAI therapy in post-thyroidectomy patients.
authors.affiliation: Department of Internal Medicine, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Republic of Korea; Severance Institute for Vascular and Metabolic Research, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Jung Eun
authors.initials: JE
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Seung Kyu
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Biostatistics Collaboration Unit, Gangnam Medical Research Center, Seoul, Republic of Korea.
authors.forename: Kyung Hwa
authors.initials: KH
authors.lastname: Han
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Mi Ok
authors.initials: MO
authors.lastname: Cho
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Gi Young
authors.initials: GY
authors.lastname: Yun
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ki Hyun
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea; Severance Institute for Vascular and Metabolic Research, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Hoon Young
authors.initials: HY
authors.lastname: Choi
authors.affiliation: Department of Nuclear Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Young Hoon
authors.initials: YH
authors.lastname: Ryu
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Sung Kyu
authors.initials: SK
authors.lastname: Ha
authors.affiliation: Department of Internal Medicine, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea; Severance Institute for Vascular and Metabolic Research, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Hyeong Cheon
authors.initials: HC
authors.lastname: Park
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology / Q000209:etiology*; D007457:Iodine Radioisotopes / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000150:complications / Q000532:radiotherapy* / Q000601:surgery; D013965:Thyroidectomy
chemical_list: D007457:Iodine Radioisotopes