Serum thyroid hormone and thyrotropin levels in subjects from endemic goiter regions of New Guinea.

Abstract

We studied serum thyroid hormone and thyrotropin (TSH) levels in subjects from two regions (Nomane and KarKar) of New Guinea where endemic goiter and/or iodine deficiency are prevalent. The results of the studies in 285 patients from Nomane indicated subnormal serum T4 (mean plus or minus SD, 6.5 plus or minus 2.8 vs 8.4 plus or minus 2.0 mug/1ll ml, for normal Americans, P less than 0.001), supranormal serum T3 (161 plus or minus 51 vs 126 plus or minus 33, ng/100 ml, p less than 0.001), supranormal serum T3/T4 ratio (T3/T4 x 100, 3.1 plus or minus 2.4 vs 1.5 plus or minus 0.4, P less than 0.001) and supranormal serum TSH (16 plus or minus 40 vs 2.7 plus or minus 1.2 muU/ml, P less than 0.001). Serum free T4 and free T3 were measured in 42 subjects. Serum free T4 was subnormal (2.0 plus or minus 0.9 vs 2.8 plus or minus 0.5, ng/100 ml P less than 0.001) and free T3 was elevated (677 plus or minus 150 vs 375 plus or minus 105, pg/100 ml, P less than 0.001). Serum T4 in goitrous patients was significantly lower than that in non-goitrous patients (5.9 vs 6.9 mug/100 ml, P less than 0.005). However, serum T3 and TSH were no different in the presence or absence of goiter. The frequencies of elevated serum TSH or serum T3 in presence of goiter were also no different from those in its absence. The mean values of various thyroid function tests in 37 subjects from KarKar Island were similar to the corresponding values in Nomane subjects. Serum T4, T3 and TSH values in 8 of 13 deaf-mute patients were similar to the corresponding mean values of other inhabitants of the region. However, the remaining 5 patients had deaf-mutism with no appreciable abnormality in thyroid function. Serum TSH correlated inversely with serum T4 (r= -0.31, P less than 0.001). There was, however, no significant relationship between serum TSH and T3 levels. The data suggest that: 1) circulating T4 exerts a significant negative feedback effect on serum TSH level and that this effect of T4 may be even more important than that of circulating T3; 2) factors other than hypothyroidism may be important in the genesis of neurological defects in endemic goiter regions.