title: [Determination of urinary iodine concentration by inductively coupled plasma-mass spectrometry in thyroid cancer patients on low-iodine diet].
abstract: BACKGROUND
  Thyroid cancer patients should be on low-iodine diet (LID) before radioactive iodine therapy (RAIT) to maximize the effect of RAIT. Urinary iodine excretion is the most accurate marker of very recent dietary iodine intake. We developed and evaluated the analytical performance of inductively coupled plasma-mass spectrometry (ICP-MS) to determine urinary iodine concentration.
  
  
  METHODS
  We evaluated the linearity, precision, accuracy, and lower limit of quantification (LLOQ) of an ICP-MS method (Agilent 7500ce) to determine urinary iodine concentration in accordance with the Food and Drug Administration (FDA) guidelines for bioanalytical method validation. This method was used to determine and compare the iodine concentration in random urine samples of 120 thyroid cancer patients on LID for 1 week and 80 healthy adults on normal diet.
  
  
  RESULTS
  Our ICP-MS method showed good linearity (1.0-1,913 microg/L; R(2)>0.999). Both intra-day and inter-day precision CV were within 20% for the LLOQ (1 microg/L) and within 15% for the other concentrations. Accuracy was 110-120% for the LLOQ and 95-115% for the other concentrations. The median concentration of iodine in random urine samples from thyroid cancer patients on LID (38.7 microg/L) was significantly lower than that of healthy subjects (238.8 microg/L) (P<0.0001).
  
  
  CONCLUSIONS
  Urinary iodine analysis by ICP-MS showed good linearity, precision, accuracy, wide measuring range of detection, and lower LLOQ. This method will be very useful to evaluate the status of dietary iodine intake and the appropriateness of LID in thyroid cancer patients, thereby maximizing the effect of RAIT.
authors.affiliation: Department of Laboratory Medicine & Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Lee
authors.forename: Ok Ja
authors.initials: OJ
authors.lastname: Ji
authors.forename: Min Jung
authors.initials: MJ
authors.lastname: Song
authors.forename: Hyung Doo
authors.initials: HD
authors.lastname: Park
authors.forename: Hee Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Sun Wook
authors.initials: SW
authors.lastname: Kim
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Chung
authors.forename: Soo Youn
authors.initials: SY
authors.lastname: Lee
mesh_terms: D000328:Adult; D004032:Diet; D005260:Female; D006801:Humans; D007455:Iodine / Q000652:urine*; D057230:Limit of Detection; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D008875:Middle Aged; D015203:Reproducibility of Results; D013964:Thyroid Neoplasms / Q000532:radiotherapy* / Q000652:urine
chemical_list: D007455:Iodine