USE OF PLASMA IODINE ASSAY FOR DIAGNOSING THYROID-DISORDERS

Aims-To examine the advantage of systematic plasma iodine assays in establishing the thyroid function of patients with thyroid disorders. Methods-Iodine was determined by inductively coupled plasma mass spectrometry (ICPMS) in the plasma of 799 patients consulting for possible thyroid disorders, indicated by FT4 and TSH assays. Results-Plasma iodine was below 40 mug/l in 57 (7%) patients, most of whom had hypothyroidism; 40-80 mug/l in 439 (55%) patients, most of whom had normal thyroid hormone function; 80-250 mug/l in 240 (30%) patients, most of whom had hyperthyroidism; and above 250 mug/l in 63 (8%) patients, almost all of whom had iodine overload caused by iodinated drugs, particularly amiodarone, resulting in euthyroidism (24%), hyperthyroidism (36%), and hypothyroidism, (16%). Sixty five (7%) had been treated with amiodarone and 27 (3%) with other iodinated drugs. More than 10% of patients with thyroid disorders therefore had an iodine overload. Conclusions-The determination of total plasma iodine using the simple, accurate ICPMS technique, should be carried out in patients consulting for thyroid disorders, particularly for the detection of an iodine overload.