title: Usefulness of iodine/creatinine ratio from spot-urine samples to evaluate the effectiveness of low-iodine diet preparation for radioiodine therapy.
abstract: OBJECTIVE
  The success of a low-iodine diet (LID) is best determined by measurement of 24-h urine iodine (U-I) excretion. The aim of this study was to determine reliable estimates for 24-h U-I based on spot-urine samples and to provide cut-offs to determine the effectiveness of LID preparation.
  
  
  METHODS
  We prospectively measured iodine levels in 193 patients based on 24-h- and spot-urine samples before radioactive iodine therapy. The iodine was expressed as the 24-h U-I excretion (microg/day) and as two different indices from spot urine, simple iodine concentration (simple I) and the iodine/creatinine (I/Cr) ratio. Poor LID preparation was defined as I excretion of >150 microg/day according to the 24-h U-I measurement.
  
  
  RESULTS
  The measured 24-h U-I was significantly higher than the two indices from spot urine (P < 0.001). However, there were statistically significant correlations between the 24-h U-I values and the two spot-urine-based indices; the correlation coefficient was 0.539 for simple I and 0.773 for I/Cr ratio (P < 0.001). The cut-off of I/Cr ratio for poor LID preparation was >66.2 microg/g Cr (sensitivity 96.4%, specificity 83.6%, positive predictive value 50.0% and negative predictive value 99.3%).
  
  
  CONCLUSIONS
  We demonstrated that the I/Cr ratio from spot urine could serve as a useful and reliable alternative to 24-h urine collection as it has acceptable diagnostic values for detecting poor LID preparation.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul, Korea.
authors.forename: Hee Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Soo Youn
authors.initials: SY
authors.lastname: Lee
authors.forename: Ji In
authors.initials: JI
authors.lastname: Lee
authors.forename: Hye Won
authors.initials: HW
authors.lastname: Jang
authors.forename: Soo Kyoung
authors.initials: SK
authors.lastname: Kim
authors.forename: Hye Soo
authors.initials: HS
authors.lastname: Chung
authors.forename: Alice Hyun Kyung
authors.initials: AH
authors.lastname: Tan
authors.forename: Kyu Yeon
authors.initials: KY
authors.lastname: Hur
authors.forename: Jae Hyeon
authors.initials: JH
authors.lastname: Kim
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Chung
authors.forename: Sun Wook
authors.initials: SW
authors.lastname: Kim
mesh_terms: D000328:Adult; D003404:Creatinine / Q000652:urine*; D004032:Diet; D005260:Female; D006801:Humans; D007455:Iodine / Q000008:administration & dosage / Q000652:urine*; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D016482:Urinalysis / Q000379:methods
chemical_list: D007457:Iodine Radioisotopes; D007455:Iodine; D003404:Creatinine