Comparativa de los métodos de evaluación de la reserva de yodo corporal previamente a la realización de tratamiento con radioyodo

Introduction and Objectives

Radioactive iodine therapy (RAIT) is recommended to reduce the risk of recurrence and metastasis in patients with intermediate-high risk differentiated thyroid cancer (DTC). In preparation for RAIT, stimulation of thyroid-stimulating hormone and reduction of body iodine pool are important for treatment success. For this purpose, patients are asked to reduce their iodine intake before RAIT, and the body iodine pool can be evaluated by measuring iodine excretion in urine before treatment. The aim of our study is to compare the methods used to measure the body iodine pool in the evaluation of the restricted iodine diet (RID) effectiveness applied in the RAIT preparation.

Patients and methods

Eighty DTC patients discontinued levothyroxine three weeks before RAIT and followed up with a RID two weeks before treatment. After two weeks of RID, all patients collected their 24-hour urine the day before the RAIT date. Patients completed 24-hour urine samples on the morning of the RAIT date and also provided a spot urine sample. The estimated 24-hour creatinine excretion of the patients was calculated. Estimated 24-hour urinary iodine excretion (UIE) was calculated using the spot urine iodine/creatinine (I/C) ratio of the patients. 24-hour UIE, iodine concentration in spot urine, I/C ratios in spot urine and estimated 24-hour UIE of the patients were analyzed by comparing with each other.

Results

In 99% of the patients, RID efficiency was sufficient according to 24-hour UIE before RAIT. The mean 24-hour UIE was 48.81 micrograms/day (mcg/day) in 24-hour urine samples taken from the patients to evaluate the body iodine pool. The patients’ iodine concentrations in spot urine, I/C ratios in spot urine, and estimated 24-hour UIE were all statistically significantly lower than actual 24-hour UIE, which was the reference method (p: 0.026 vs <0.001 vs 0.041). Moderate positive correlation between 24-hour UIE and iodine concentration in spot urine (r: 0.440), I/C ratio in spot urine (r: 0.493), and estimated 24-hour UIE (r: 0.560) found. The strongest correlation was obtained with the estimated 24-hour UIE.

Conclusion

The estimated 24-hour UIE obtained by using the I/C ratio in spot urine can be used practically and safely as an alternative to UIE in 24-hour urine, which is the gold standard method for evaluating body iodine pool.