Relationship between serum thyroglobulin and intrathyroidal stable iodine in human simple goitre

Serum thyroglobulin levels are increased in many patients with simple goitre. This increase has been attributed to the release of thyroglobulin (Tg) from the colloid of necrosed follicles. To test the hypothesis that increased serum Tg could be related to the low intrathyroidal iodine concentration [I], the main cause of nontoxic goitre, these two variables were measured in 91 euthyroid goitrous patients and compared to serum free T3 and free T4 levels as well as thyroid weight. Thyroid iodine concentration was estimated from the X-ray fluorescence measurement of intrathyroidal iodine stores and from the weight of the gland estimated by planimetry. Serum Tg levels, the free T3/T4 ratio and thyroid weight were negatively correlated to [I] (Spearman's coefficient of correlation = - 0.44 (P = 0.001); -0.30 (P = 0.006); -0.33 (P = 0.001), respectively). Tg levels were also positively correlated to the T3/T4 ratio (R = 0.28, P = 0.008) and to the weight of the gland (R = 0.37; P = 0.001). These data suggest that, in simple goitre, increased serum Tg concentrations are partly related to the reduced concentration of iodine in goitre tissue (as are an increased T3/T4 ratio and the size of the goitre) and is not only the reflection of follicular necrosis.