54 population. Thefindings also support the program of thyroxine replacementin the exposed Rongelap population to prevent both clinical hypothyroidism and the associatedrise in plasma TSH, which was significantly lower (6.04 1.8 ug/dl). The frequencydistribution calculations (see Table 29 and Figure 39) indicate that a substantial portion of the Utirik population has plasma T, concentra- 4. Thyroid Function in the Utirik and iodothvronine (not shown) showedsimilar reductions in those patients with low Ty values. Plasma. may be tumorigenic. Unexposed Rongelap Groups tion <3 pg/dl. Measurements of plasma tri- During the 1973 survey, T4 and TSH concentrations were measuredin plasma from [09 unexposed Rongelap and 97 exposed Utirik subjects 40 a---e Utirik March 1973 Rongelap group, 7.7 ug/dl, was the sameas in the United States, and, as in the United States, in Utirik and Unexposed Rongelap Populations, March 1973 Plasma Ts, Group ug/dl 109 Rongelap unexposed 97 Utirik exposed Subjects tw S Plasma Thyroxine Concentrations (Mean + S.D.) 30 % oftotal population Tabie 29 Subjects with value with value <5.0. 1L0e >I1ES 7,742.0 6% 6% 6.0 1.8* 32%** 6% 25 *Significantly different, p<.0.001. **6% had values <3.8. Thyroxine-Binding Globulin (TBG) Levels Rongelap Exposed Unexposed All sera All sera* Uurik All sera All sera* 75 TBG (RIA) (Mean = S.D.) tn Serum, 1973 Group 5.0 10.0 Plasma thyroxine (ug/100 ml} 12.5 Figure 39. Percentages of people in Utirik and in Rongelap unexposed groups having given thyroxinelevels, 1973. Table 30 TBG by RIA T e——e Rongelap (see Table 29). The mean Ty; in the unexposed the plasma T4 concentrations were skewedto the upper range. In the Utirik group, the mean Ty T TBG capacity — TBG-binding capacity n mg/dl n ug T,/dl 12 13 29 22 1.45+0.54 1.82+1.22 1.64+0.95 1,340.45 14 1100 25 2b 215+ 69 25.32015.7 23.b4115 19.1> 6.2 22 22 1.4020.42 1.40+0.42 31 27) 189+ 78 16.44% 43 *Omitting sera with TBG >3 or TBG-binding capacity > 30. Statistical comparisons revealed no significant difference (p>>0.05) between any of the groups. 45+ q i ! i i | I 0 1 2 3 4 5 mg/dl O 10 20 30 pg T?/dl / 40 30 Figure 40. Thyroxine-bindingglobulin levels in serum and TBG-binding capacity, 1973.