Summary
Twenty-five patients with nodular goitre who had thyroid hormone levels within normal
ranges and an absent thyrotropin (TSH) response to TSH releasing hormone (TRH) as
measured by a conventional radioimmunoassay with a lower detection limit of 0.6 mU/l
were studied. Based on these data, and the clinical evaluation patients were divided
into a hyperthyroid group (n=12) and a euthyroid group (n=13). The samples from the
TRH test were reanalyzed by an immunoradiometric TSH assay with a detection limit
of 0.05 mU/l.
Basal serum TSH showed a considerable overlap between the two groups, but values above
0.10 mU/l were always associated with euthyroidism. Using this level of discrimination
76% of the patients were correctly classified. A TSH response to TRH of 0.10 mU/l
provided a better discrimination allowing a correct diagnosis in 92% of the patients.
It is concluded that serum TSH as measured by a sensitive assay is suitable as a first
line test in patients with nodular goitre. However, patients with basal serum TSH
levels below 0.10 mU/l need further investigation with a TRH-test. A TSH response
to TRH above 0.10 mU/l seems to secure euthyroidism, whereas lower responses almost
always are associated with hyperthyroidism.
Key-Words
TSH Response to TRH
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Nodular Goitre
