Abstract
The aim of the study was to evaluate thyroid-stimulating hormone (TSH) concentration
in a reference group and to compare it with the TSH in subjects with high probability
of thyroid dysfunction. The study population consisted of 852 subjects. The reference
group consisting of 316 subjects was obtained by the exclusion of the subjects having
thyroid disease, taking thyroid influencing drugs, having increased thyroid peroxidase
(TPO) antibodies, or having abnormal thyroid ultrasound. 42 high probability of thyroid
dysfunction subjects were defined by the association of increased TPO antibody concentration,
changed echogenicity, and changed echosonographic structure of thyroid parenchyma.
In the reference group TSH reference range was 0.45 mU/l (95% CI 0.39–0.56 mU/l) to
3.43 mU/l (95% CI 3.10–4.22 mU/l). To distinguish reference and high probability of
thyroid dysfunction group a TSH threshold was calculated. At a threshold value of
3.09 mU/l (95% CI 2.93–3.38 mU/l), specificity was 95% and sensitivity 38.1%. Using
2 different approaches to find upper limit of the TSH reference range we obtained
similar results. Using reference group only a value of 3.43 mU/l was obtained. Using
both reference group and subjects with the high probability of thyroid dysfunction
we obtained 95% CI for the upper reference limit between 2.93 and 3.38 mU/l. Based
on these premises, it could be argued that conservative estimate of the TSH upper
reference range should be 3.4 mU/l for both sexes.
Key words
thyrotropin - antibodies to thyroid peroxidise - hypothyroidism
