Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

STSH
8939
TSI
8634
Thyroid-Stimulating Hormone-Sensitive (s-TSH), Serum
Clinical Information: Thyroid-stimulating hormone (TSH) is a glycoprotein hormone that has 2
subunits. The alpha-subunit is similar to those of follicle-stimulating hormone, human chorionic
gonadotropin, and luteinizing hormone. The beta-subunit is different from those of the other
glycoprotein hormones and confers its biochemical specificity. TSH is synthesized and secreted by the
anterior pituitary in response to a negative feedback mechanism involving concentrations of free
triiodothyronine and free thyroxine. Additionally, the hypothalamic tripeptide, thyrotropin-releasing
hormone, directly stimulates TSH production. TSH interacts with specific cell receptors on the thyroid
cell surface and gives rise to 2 main actions. First, it stimulates cell reproduction and hypertrophy.
Second, it stimulates the thyroid gland to synthesize and secrete triiodothyronine and thyroxine. In
primary hypothyroidism, TSH levels will be elevated. In primary hyperthyroidism, TSH levels will be
low. See Thyroid Function Ordering Algorithm in Special Instructions.
Useful For: Monitoring patients on thyroid replacement therapy Confirmation of thyroid-stimulating
hormone (TSH) suppression in thyroid cancer patients on thyroxine therapy Prediction of
thyrotropin-releasing hormone-stimulated TSH response An aid in the diagnosis of primary
hyperthyroidism Differential diagnosis of hypothyroidism
Interpretation: The ability to quantitate circulating levels of thyroid-stimulating hormone (TSH) is
important in evaluating thyroid function. It is especially useful in the differential diagnosis of primary
(thyroid) from secondary (pituitary) and tertiary (hypothalamus) hypothyroidism. In primary
hypothyroidism, TSH levels are significantly elevated, while in secondary and tertiary hypothyroidism,
TSH levels are low or normal. Concentrations of 5.1 mIU/L to 7.0 mIU/L are considered borderline
hypothyroid. For primary hyperthyroidism, a high-sensitivity TSH assay is required to detect the
decrease in TSH with sufficient diagnostic accuracy. This assay is an enhanced version of the sensitive
TSH assay, and has a sensitivity down to 0.002 mIU/L. Thyrotropin-releasing hormone (TRH)
stimulation differentiates all types of hypothyroidism by observing the change in patient TSH levels in
response to TRH. Typically, the TSH response to TRH stimulation is exaggerated in cases of primary
hypothyroidism, absent in secondary hypothyroidism, and delayed in tertiary hypothyroidism. Most
individuals with primary hyperthyroidism have TSH suppression and do not respond to TRH
stimulation test with an increase in TSH over their basal value. Based on a study at Mayo Clinic, if the
s-TSH result is < or =0.1 mIU/L, there is only about a 1% chance the patient will respond to a TRH
stimulation test. Patients with s-TSH values between 0.1 to 0.4 mIU/L sometimes respond, whereas
patients with values > or =0.4 mIU/L will have a complete or partial response to TRH.
Reference Values:
> or =12 months: 0.3-5.0 mIU/L
Reference values have not been established for patients that are less than 12 months of age.
Clinical References: 1. Fatourechi V, Lankarani M, Schryver P, et al: Factors influencing clinical
decisions to initiate thyroxine therapy for patients with mildly increased serum thyrotropin (5.1-10.0
mIU/L). (Journal Article) Mayo Clin Proc 2003 May;78(5):554-560 2. Klee G, Hay I: Biochemical
testing of thyroid function. Review. Endocrinol Metab Clin North Am 1997 Dec:26(4):763-775 3.
Wilson J, Foster D, Kronenburg MD H, et al: Textbook of Endocrinology. 9th edition, WB Saunders
Company, 1998
Thyroid-Stimulating Immunoglobulin (TSI), Serum
Clinical Information: Autoimmune thyroid disease is characterized by the presence of
autoantibodies against various thyroid components, namely the thyrotropin receptor (thyroid-stimulating
hormone receptor [TSHR]), thyroid-peroxidase (TPO), and thyroglobulin (Tg), as well as an
inflammatory cellular infiltrate of variable severity within the gland. Among the autoantibodies found in
autoimmune thyroid disease, TSHR autoantibodies are most closely associated with disease
pathogenesis. All forms of autoimmune thyrotoxicosis (Graves disease, Hashitoxicosis, neonatal
thyrotoxicosis) are caused by the production of TSHR-stimulating autoantibodies. The role of the TPO
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