Serum thyroxine and age--rather than thyroid volume and serum TSH--are determinants of the thyroid radioiodine uptake in patients with nodular goiter.
BACKGROUND
Radioiodine (131I) therapy is widely used for treatment of non-toxic goiters. A limitation for this treatment is a low thyroid radioiodine uptake (RAIU), often encountered in these patients.


OBJECTIVE
To estimate the impact of various factors on the thyroid RAIU.


METHODS
We examined prospectively 170 patients (146 females; age range: 22-87 yrs) with nodular goiter (median 64 ml, range: 20-464 ml) selected for 131I therapy. Serum TSH was sub-normal in 42.4%. None were treated with anti-thyroid drugs. The thyroid RAIU was determined at 24h and 96 h. The goiter volume was measured by ultrasound (no.=127), or by magnetic resonance imaging (no.=43).


RESULTS
The 24h and the 96 h RAIU were 34.2 ± 9.8(SD)% (range: 11.4-66.0%) and 34.0 ± 10.0% (range: 10.5-60.9%), respectively. Sixty-one patients had a 24h RAIU <30% and these individuals were older than patients with a 24h RAIU ≥ 30% (median 58 vs 51 yrs, p=0.02). These two subgroups did not differ significantly in other variables. Overall, the 24h RAIU was positively correlated to the serum (s) free T4-index (r=0.20, p=0.01), and negatively to age (r=-0.18, p=0.02), but not significantly related to serum TSH or thyroid volume. Age correlated positively with thyroid volume (r=0.31, p < 0.001). In a regression analysis, s-free T4-index and age remained as the only determinants of the 24h and the 96 h RAIU.


CONCLUSIONS
In patients with a symptomatic nodular goiter, serum T4 and age are the major determinants of the thyroid RAIU. A sub-normal serum TSH is not a marker of a compromised thyroid RAIU but reflects that the iodine is confined to a few 'hot spots'.
Bonnema
S J
SJ
Department of Endocrinology, Odense University Hospital, DK-5000 Odense C, Denmark. steen.bonnema@dadlnet.dk
Fast
S
S
Nielsen
V E
VE
Boel-Jørgensen
H
H
Grupe
P
P
Andersen
P B
PB
Hegedüs
L
L
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D005260:Female; D006044:Goiter, Nodular / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism* / Q000627:therapeutic use; D008875:Middle Aged; D011446:Prospective Studies; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000378:metabolism* / Q000473:pathology* / Q000528:radiation effects; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D055815:Young Adult
D007457:Iodine Radioisotopes; D013972:Thyrotropin; D013974:Thyroxine