A critical appraisal of goiter assessment and the ratio of urinary iodine to creatinine for evaluating iodine status

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Abstract
Iodine status can be evaluated by goiter assessment and measurement of urinary iodine concentration in either 24-h urine collections or in casual samples. It is often impossible to make 24-h collections. Therefore, iodine concentration in casual samples is often expressed in terms of urinary creatinine, assuming creatinine excretion to be constant between and within individuals. In this study large inter- and intraindividual variations were observed in the creatinine content of casual samples ranging from 0.6 to 9.87 mmol/L. Further, the urinary iodine-creatinine ratio correlated significantly with the creatinine concentration; Spearman's rank-order correlation coefficient, rs= 0.39 (P < 0.001). If creatinine is a suitable index to correct for variations in iodine excretion, no correlation would be expected. We conclude that the iodine-creatinine ratio in casual urine samples is an unsuitable indicator for evaluating iodine status in areas where large inter- and intraindividual variations in urinary creatinine excretion exist.