Korean J Lab Med.  2010 Aug;30(4):351-356. 10.3343/kjlm.2010.30.4.351.

Determination of Urinary Iodine Concentration by Inductively Coupled Plasma-mass Spectrometry in Thyroid Cancer Patients on Low-iodine Diet

• Lee JH
• Ji OJ
• Song MJ
• Park HD
• Kim HK
• Kim SW
• Chung JH
• Lee SY

• KMID: 1781640
• DOI: http://doi.org/10.3343/kjlm.2010.30.4.351

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 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.

Keyword

ICP-MS; Urinary iodine; Low-iodine diet; Radioactive iodine therapy; Thyroid cancer

MeSH Terms

Adult
Diet
Female
Humans
Iodine/*urine
Limit of Detection
Male
Mass Spectrometry/*methods
Middle Aged
Reproducibility of Results
Thyroid Neoplasms/*radiotherapy/urine

Figure

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  Fig. 1. Linearity of standard iodine obtained by using inductively coupled plasma-mass spectrometry (ICP-MS).

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  Fig. 2. Distribution patterns of urinary iodine in normal adults and thyroid cancer patients on low-iodine diet. Abbreviation: ICP-MS, inductively coupled plasma-mass spectrometry.

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