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 microgram/L; R2>0.999). Both intra-day and inter-day precision CV were within 20% for the LLOQ (1 microgram/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 microgram/L) was significantly lower than that of healthy subjects (238.8 microgram/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.
Adult ; Diet ; Female ; Humans ; Iodine/*urine ; Limit of Detection ; Male ; Mass Spectrometry/*methods ; Middle Aged ; Reproducibility of Results ; Thyroid Neoplasms/*radiotherapy/urine

PURPOSE: The radioiodine ablation therapy is required for patients who underwent a total thyroidectomy. Through a comparative review of a low iodine diet (LID) and a restricted iodine diet (RID), the study aims to suggest guidelines that are suitable for the conditions of Korea. MATERIALS AND METHODS: The study was conducted with 101 patients. With 24-hour urine samples from the patients after a 2-week restricted diet and after a 4-week restricted diet, the amount of iodine in the urine was estimated. The consumed radioiodine amounts for 2 hours and 24 hours were calculated. RESULTS: This study was conducted with 47 LID patients and 54 RID patients. The amounts of iodine in urine, the 2-week case and 4-week case for each group showed no significant differences. The amounts of iodine in urine between the two groups were both included in the range of the criteria for radioiodine ablation therapy. Also, 2 hours and 24 hours radioiodine consumption measured after 4-week restrictive diet did not show statistical differences between two groups. CONCLUSION: A 2-week RID can be considered as a type of radioiodine ablation therapy after patients undergo a total thyroidectomy.
Ablation Techniques ; Adult ; Carcinoma/metabolism/*radiotherapy/surgery ; *Diet ; Female ; Humans ; Iodides/urine ; Iodine/administration & dosage/urine ; Iodine Radioisotopes/metabolism/*therapeutic use ; Male ; Middle Aged ; Republic of Korea ; Thyroid Neoplasms/metabolism/*radiotherapy/surgery ; Thyroidectomy ; Treatment Outcome