Re-establishment of normal radioactive iodine uptake reference range in the era of universal salt iodization in the Indian population

BACKGROUND & OBJECTIVES: The reference radioactive iodine uptake (RAIU) values established in the 1970s in the era of widespread iodine deficiency were relatively high. Now, after four decades of successful Universal Salt Iodization (USI) programme in India, there is a need to re-establish these reference ranges. The present study was aimed to quantify the two-hour and 24-h RAIU values in iodine sufficient euthyroid individuals and validate the results in Graves’ and Hashimoto's thyroiditis patients. METHODS: In this prospective study conducted from April 2012 to September 2013, euthyroid volunteers who consented for the investigations were enrolled in the study. Treatment-naive Graves’ disease and Hashimoto's thyroiditis patients were recruited from the outpatient clinic. The investigations included neck ultrasonography, thyroid function tests, thyroglobulin (Tg), anti-Tg and anti-thyroid peroxidase antibody and urinary iodine concentration. RESULTS: Three different groups comprising 110 euthyroid volunteers, 38 Graves’ and 17 Hashimoto's thyroiditis patients were enrolled in the study. The mean 2-h RAIU values for the euthyroid group, Hashimoto's thyroiditis and Graves’ patients were 3.83±2.77, 4.22±3.41 and 32.67±15.93 per cent, and mean 24-h RAIU values were 12.75±5.51, 11.66±9.55 and 61.85±12.9 per cent, respectively. The mean thyroid volumes were 7.63±2.72, 7.81±1.67 and 20.76±12.56 ml for the euthyroid, Hashimoto's thyroiditis and Graves’ disease groups and the mean spot urinary iodine concentrations were 9.0, 7.8 and 13.9 µg/dl in the three groups, respectively. The new reference range (95% confidence interval) for two-hour was 1-7 per cent and 24-h was 7-18 per cent. INTERPRETATION & CONCLUSIONS: Compared to the previous values, there was a considerable decrease in the RAIU values in euthyroid individuals. This was further corroborated with increase in the urinary iodine concentration and decrease in thyroid volume, attributed to successful USI programme. Further studies with a large sample from different parts of India need to be done to confirm these findings.