P12 - Morning spot urine iodine-to-creatinine ratio as a surrogate for 24-hour iodine excretion in adult non-pregnant women

Background/Introduction A reliable assessment of iodine status is essential to prevent thyroid dysfunction. Urinary iodine concentration (UIC) from spot samples is commonly used, but high variability limits its diagnostic performance. Purpose This study evaluated whether the iodine-to-creatinine ratio (UI/CR) in morning spot urine better reflects 24-hour urinary iodine excretion (UIE) in non- pregnant adult women. Methods We enrolled 49 women undergoing endocrine evaluation. Each participant provided a morning spot urine sample and a complete 24-hour urine collection. Iodine and creatinine levels were measured to calculate UI/CR. ROC analysis was used to determine the diagnostic performance of morning UI/CR in identifying iodine deficiency. Results Only 16.3% of participants had adequate iodine excretion (≥150 µg/day), and more than half (55.1%) had values <100 µg/day. No correlation was observed between spot UIC and 24-hour UIE (r = 0.20; p = 0.18), while morning UI/CR correlated weakly but significantly with 24-hour UIE (r = 0.21; p < 0.001). A cut-off value of ≤0.73 µg/L/mg/dL for UI/CR identified iodine deficiency (<100 µg/day) with 66.7% sensitivity and 72.7% specificity. Conclusion(s) The iodine-to-creatinine ratio in morning spot urine serves as a more stable estimate of iodine status than iodine concentration. Although its sensitivity for detecting mild insufficiency is low, UI/CR is a practical and cost-effective alternative when 24-hour collection is not possible, especially for identifying more severe iodine deficiency.