Thyroid Research Thyroid Research Archive Thyroid Disease

Unselected healthy subjects and healthy subjects with no risk factors for thyroid disorders have similar serum thyrotropin concentrations

(November 2005)

The background of the study. This study was done to determine whether the serum concentrations of thyrotropin (TSH) and free thyroxine (T4) were different in healthy subjects and in a subgroup of these subjects formed by excluding subjects who might have a thyroid disorder.

How the study was done. The main study group consisted of 870 blood donors (425 women, 445 men). Among them, 443 (51 percent) had no family history of thyroid disorders, normal thyroid ultrasonography, and no evidence of thyroid autoimmune disease. Serum TSH and free T4 were measured in all subjects.

The results of the study. The serum TSH and free T4 concentrations in the complete group and the subgroup with no risk factors for thyroid disease were similar, except that the calculated lower limit (2.5th percentile) for serum TSH was slightly lower in the complete group (Table).

Table. Median (2.5th to 97.5th Percentile) Serum TSH and Thyroid Hormone Concentrations in the Complete Group (n = 870) and the Subgroup with No Risk Factors for Thyroid Disorders (n = 453).
	Complete Group	Subgroup
Serum TSH (mU/L)	1.31 (0.30–3.63)	1.36 (0.40–3.77)
Serum free T4 (ng/dl)	1.25 (0.98–1.61)	1.25 (0.99–1.58)

The conclusions of the study. Serum TSH and free T4 concentrations are virtually identical in healthy subjects and in healthy subjects with no family history of thyroid disease, normal thyroid ultrasonography, and no thyroid autoimmunity. The presence of subjects with these risk factors for thyroid disorders among subjects whose values determine the normal range does not distort that range.

The original article. Kratzsch J, Fiedler GM, Leichtle A, Brugel M, Buchbinder S, Otto L, Sabri O, Matthes G, Thiery J. New reference intervals for thyrotropin and thyroid hormones based on National Academy of Clinical Biochemistry Criteria and regular ultrasonography of the thyroid. Clin Chem 2005;51:1480-6.