title: A low incidence of iodine-induced hyperthyroidism following administration of iodinated contrast in an iodine-deficient region.
abstract: OBJECTIVE
  There are limited data on the incidence of iodinated contrast-induced thyrotoxicosis, particularly in iodine-deficient regions. The aim of this study was to determine the incidence of iodinated contrast-induced thyrotoxicosis and to determine whether thyrotoxicosis was more common in patients ≥70 years compared to those <70 years of age.
  
  
  METHODS
  A prospective study of adult patients undergoing an outpatient CT with iodinated contrast was performed.
  
  
  METHODS
  Thyroid function tests (TFTs) and urine iodine measurements were performed prior to the scan. TFTs were repeated at 4- and 8-weeks postscan. Changes in TFTs from baseline were analysed.
  
  
  RESULTS
  A total of 102 patients were included in the final analysis. Overall, TSH levels dropped (P = 0·0002), and free T3 (FT3 ) levels increased (P = 0·04) between baseline and week 4 with normalization by week 8; however, these changes were not considered clinically significant. No significant differences in free T4 (FT4 ) occurred in the overall group (P = 0·82). There were no differences in TFTs between baseline and 4 or 8 weeks for those patients aged <70 compared to ≥70 years. Two patients developed new subnormal TSH values. Of these, one had a 90-mm follicular variant papillary thyroid carcinoma diagnosed while the other had a normal thyroid assessment and TSH spontaneously normalized by 12 weeks.
  
  
  CONCLUSIONS
  Only 2% of patients developed subclinical hyperthyroidism following a standard dose of iodinated contrast for CT investigations. Given the low incidence of iodine-induced thyrotoxicosis, there is no indication for routine pre- and post-CT thyroid function testing in our region.
authors.affiliation: Department of Endocrinology, Waikato Hospital, Hamilton, New Zealand.
authors.forename: Carol
authors.initials: C
authors.lastname: Jarvis
authors.affiliation: Department of Radiology, Waikato Hospital, Hamilton, New Zealand.
authors.forename: Kim
authors.initials: K
authors.lastname: Simcox
authors.affiliation: Department of Endocrinology, Waikato Hospital, Hamilton, New Zealand.
authors.forename: Jade A U
authors.initials: JA
authors.lastname: Tamatea
authors.affiliation: Department of Radiology, Waikato Hospital, Hamilton, New Zealand.
authors.forename: Kim
authors.initials: K
authors.lastname: McAnulty
authors.affiliation: Department of Surgery, Waikato Hospital, Hamilton, New Zealand.|Waikato Clinical School, Faculty of Medical and Health Science, University of Auckland, Hamilton, New Zealand.
authors.forename: Goswin Y
authors.initials: GY
authors.lastname: Meyer-Rochow
authors.affiliation: Department of Endocrinology, Waikato Hospital, Hamilton, New Zealand.
authors.forename: John V
authors.initials: JV
authors.lastname: Conaglen
authors.affiliation: Department of Endocrinology, Waikato Hospital, Hamilton, New Zealand.|Waikato Clinical School, Faculty of Medical and Health Science, University of Auckland, Hamilton, New Zealand.
authors.forename: Marianne S
authors.initials: MS
authors.lastname: Elston
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media / Q000008:administration & dosage / Q000506:poisoning*; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000139:chemically induced* / Q000453:epidemiology; D015994:Incidence; D007455:Iodine / Q000172:deficiency* / Q000506:poisoning* / Q000652:urine; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D010045:Outpatients / Q000706:statistics & numerical data; D011446:Prospective Studies; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000032:analysis; D013974:Thyroxine / Q000032:analysis; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014284:Triiodothyronine / Q000032:analysis
chemical_list: D003287:Contrast Media; D014284:Triiodothyronine; D013972:Thyrotropin; D007455:Iodine; D013974:Thyroxine