Evaluation of thyrotropin secretion before and after TRH by third generation chemiluminescent assay. Assessment of subclinical hyperthyroidism.
The recent introduction of third generation assays for TSH has led to a considerable improvement of assay sensitivity. To assess the clinical significance of subnormal basal TSH (b-TSH) values (< 0.2 microU/ml), we investigated b-TSH and TRH-stimulated TSH (r-TSH) by means of a new, highly sensitive immunochemiluminometric assay in 105 euthyroid subjects, 45 patients with overt hyperthyroidism and 18 patients suspected of having subclinical hyperthyroidism. A weak, albeit statistically significant, correlation (r = 0.48) was found between b-TSH and r-TSH and also between b-TSH and delta-TSH (r = 0.31) in euthyroid subjects. Consideration of b-TSH alone correctly identified 90 % of euthyroid subjects in this group; 10 of 105 apparently euthyroid subjects presented delta-TSH suggesting subclinical hyperthyroidism. While b-TSH was detectable (> 0.04 microU/ml) in 8 of 45 (18%) of hyperthyroid patients, all (100%) were abnormal in both b-TSH and r-TSH. 14 of 18 (78%) of patients with subclinical hyperthyroidism exhibited a blunted TSH response to stimulation (delta-TSH < 2 microU/ml). These results suggest that although the new generation of TSH assays can be a valuable addition to the diagnostic arsenal of thyroid function tests, certain limitations must still be accepted. Specifically, b-TSH in the "grey zone" (0.1-0.2 microU/ml) appears to be a less than reliable predictor of thyroid function.
Duntas
L
L
Abteilung Innere Medizin I, Universität Ulm, Germany.
Grab
B M
BM
Dominguez-Munoz
J E
JE
Nelson
D K
DK
Loos
U
U
Keck
F S
FS
D000328:Adult; D000368:Aged; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis*; D008163:Luminescent Measurements; D008875:Middle Aged; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone
D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin