USE OF PLASMA IODINE ASSAY FOR DIAGNOSING THYROID-DISORDERS

Aims-To examine the advantage of systematic plasma iodine assays in es tablishing the thyroid function of patients with thyroid disorders. Me thods-Iodine was determined by inductively coupled plasma mass spectro metry (ICPMS) in the plasma of 799 patients consulting for possible th yroid disorders, indicated by FT4 and TSH assays. Results-Plasma iodin e was below 40 mug/l in 57 (7%) patients, most of whom had hypothyroid ism; 40-80 mug/l in 439 (55%) patients, most of whom had normal thyroi d hormone function; 80-250 mug/l in 240 (30%) patients, most of whom h ad hyperthyroidism; and above 250 mug/l in 63 (8%) patients, almost al l of whom had iodine overload caused by iodinated drugs, particularly amiodarone, resulting in euthyroidism (24%), hyperthyroidism (36%), an d hypothyroidism, (16%). Sixty five (7%) had been treated with amiodar one and 27 (3%) with other iodinated drugs. More than 10% of patients with thyroid disorders therefore had an iodine overload. Conclusions-T he determination of total plasma iodine using the simple, accurate ICP MS technique, should be carried out in patients consulting for thyroid disorders, particularly for the detection of an iodine overload.