Table 8. Results of retrospective analyses suggesting the presence of thyroid dysfunction prior to surgery in certain exposed Marshallese (1980). Sub ject No. & sex 2M 19M 33F 69F 74F 83M" Date of serum sample Serum TSH (WU/m1) 1963 1963 1965 22 6.9 8.2 6.5 5.7 9.5 0.84 1.01 0.80 6.7 3.3 0.98 1966 1963 1972 1974 Normal control range: 22 470 16.3 0-6.0 Serum Ty, Cug/di1) 8.3 1.4 -- 5-10.2 TBGI (units) 0.82 0.64 -~ Age at exposure (years) Estimated thyroid dose (rads) 2 5 1100 1000 l 4 15 1150 1000 425 in utero >175 0.85-1.10 *This infant's mother (No. 74) had an estimated thyroid dose of 425 rads. It was of interest to measure TSH in frozen plasma samples obtained years earlier to determine whether individuals might have had evidence of thy- roid dysfunction prior to surgery. In many cases only one sample obtained prior to surgery was available. The criterion used in these instances was that serum TSH be >6 wU/ml on at least one occasion. It was assumed, but not proved, that TSH is relatively stable in plasma samples stored at -20°F for prolonged periods. This conclusion was supported by results on subject No. >, who had a serum TSH of 500 wU/ml in a sample obtained in 1963, but obviously it is uncertain what that value would have been had this specimen heen measured fresh. Since all subjects were on Ty, therapy after 1963, it should be assumed that these results might underestimate the prevalence of presurgical hypothyroidism. In any case, six individuals exhibited biochemical evidence of mild to severe degree of hypothyroidism prior to surgery (Table 8). The most marked abnormality was observed in subject No. 69, in whom a serum TSH of 470 wU/ml was found in a sample obtained in 1963. This subject had surgery performed in 1964. Three individuals had modest elevations in serum TSH, between 16 and 22 yU/ml, and the remaining two had mild abnormalities. Most but not all of these elevated serum TSH values were associated with decreased serum free-thyroxine indices, and all were in subjects exposed at a young age, four receiving an estimated thyroid dose >1000 rads. Receiving lower thyroid doses were No. 74, who was 15 at the time of exposure, and No. 83, who was in utero (gestational age v6 mo). These results appear to be consistent with observations in subjects No. 3 and 5. . In addition to the results on the above 13 subjects in Tables 7 and 8, which indicated primary thyroid dysfunction as a consequence of radiation aoe -73-