a+ population. Thefindings also support the program of thyroxine replacementin the exposed Rongelap population to prevent both clinical hypothyroid‘ism andthe associated rise in plasma TSH. which maybe tumorigenic. 4. Thyroid Function in the Utirik and Unexposed Rongelap_Groups During the 1973 survéy, T4 and TSH concentrations were measured in plasma from 109 unexposed Rongelap and 97 exposedUtirik subjects (see Table 29). The mean Ty in the unexposed wassignificantly lower (6.01.8 ug/dl). Thefrequencydistribution calculations (see Table 29 and Figure 39) indicate that a substantial portion of the Utirik population has plasma Ty concentra- tion <5 pe/d!l. Measurements of plasma triiodothyronine (gat shown).showedsimilar reduc- tons in those paggénts with low T, Vues. Plasma Sa ae +0 ! a---e Uurik e— Rongelap March 1973 Rongelap group, 7.7 pg/dl, was the sameas in’ the United States, and, as in the United States, the plasma 74 concentrations were skewed to the upper range. In the Utirik group, the mean T, Table 29 Plasma Thyroxine Concentrations (Mean + S.D.) in Utirik and Unexposed Rongelap Populations, March 1973 Group 109 Rongelap unexposed 97 Utirik exposed Plasma T4, pe/dl Subjects with value <5.0 Subjects with value >113 7742.0 6% 6% 6.01.8" 32%** 6% 4 T 30 F- ~ Es ol : € 2 3S 3 a & 3 Be tom 10 — — 0 25 *Significantly different, p<. 0.001. **6% had values <3.8. 50 15 10.0 Plasma thyroxine (zg/100 ml) 125 Figure 39. Percentages of people in Utirik and in Rongelap unexposed groups having given thyroxinelevels, 1973. Table 30 Thyroxine-Binding Globulin (TBG) Levels (Mean = S.D.) in Serum, 1973 TBG (RIA) r TBG by RIA rT r T ¥r TBG-binding capacity Group n mg/dl nr pe T,/dl Rongelap Exposed Unexposed All sera All sera*® 12 13 25 22 1.45+0.54 1,821.22 1.64+0.95 1.3420.45 14 110 25 21 21.5 69 .25.32215.7 23.1115 191+ 62 Utirik All sera All sera* 22 22 1.40+0.42 1.40+0.42 31 27) 18.9 78 16.4% 43 *Omitting sera with TBG>3 or TBG-binding capacity > 30. Statistical comparisons revealed nosignificant differ- ence ( p>>0.05) between anyof the groups. % a5) 20 10 5 0 o 1 3 4 5 mg/dl 2 «0 Figure 40. Thyroxine-binding globulin levels in serum and TBG-binding capacity, 1973.