Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul, Korea.
Clin Endocrinol (Oxf). 2010 Jul;73(1):114-8. doi: 10.1111/j.1365-2265.2009.03774.x. Epub 2009 Dec 29.
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.
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.
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%).
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.
低碘饮食（LID）的成功与否最好通过测量 24 小时尿碘（U-I）排泄量来确定。本研究旨在确定基于随机尿样的 24 小时 U-I 的可靠估计值，并提供确定 LID 准备效果的截止值。
我们前瞻性地测量了 193 例接受放射性碘治疗的患者的 24 小时和随机尿样中的碘水平。碘以 24 小时 U-I 排泄量（μg/天）和两种来自随机尿样的不同指标表示，即简单碘浓度（simple I）和碘/肌酐（I/Cr）比值。根据 24 小时 U-I 测量，较差的 LID 准备定义为 I 排泄量>150μg/天。
测量的 24 小时 U-I 明显高于两种随机尿样指标（P<0.001）。然而，24 小时 U-I 值与两种基于随机尿样的指标之间存在统计学上显著的相关性；简单 I 的相关系数为 0.539，I/Cr 比值的相关系数为 0.773（P<0.001）。用于检测较差 LID 准备的 I/Cr 比值的截止值为>66.2μg/g Cr（敏感性 96.4%，特异性 83.6%，阳性预测值 50.0%，阴性预测值 99.3%）。
我们证明了随机尿样的 I/Cr 比值可以作为 24 小时尿液收集的有用且可靠的替代方法，因为它具有检测较差 LID 准备的可接受的诊断价值。
