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Test ID: STSH Thyroid-Stimulating Hormone-Sensitive (s-TSH), Serum

Reporting Name

TSH, Sensitive, S

Useful For

Screening for thyroid dysfunction and detecting mild (subclinical), as well as overt, primary hypo- or hyperthyroidism in ambulatory patients

 

Monitoring patients on thyroid replacement therapy

 

Confirmation of thyrotropin (TSH, thyroid-stimulating hormone) suppression in thyroid cancer patients on thyroxine suppression therapy

 

Prediction of thyrotropin-releasing hormone-stimulated TSH response

Clinical Information

Thyrotropin (TSH, thyroid-stimulating hormone) is a glycoprotein hormone consisting of 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.

 

Serum TSH concentrations exhibit a diurnal variation with the peak occurring during the night and the nadir occurring between 10 a.m. and 4 p.m. This biological variation does not influence the interpretation of the test result since most clinical TSH measurements are performed on ambulatory patients between 8 a.m. and 6 p.m.

 

When hypothalamic-pituitary function is normal, a log/linear inverse relationship between serum TSH and free thyroxine exists.

 

See Thyroid Function Ordering Algorithm in Special Instructions.

Interpretation

In primary hypothyroidism, thyrotropin (TSH, thyroid-stimulating hormone) levels will be elevated. In primary hyperthyroidism, TSH levels will be low.

 

The ability to quantitate circulating levels of 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.

 

Elevated or low TSH in the context of normal free thyroxine is often referred to as subclinical hypo- or hyperthyroidism, respectively.

 

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 with an increase in TSH over their basal value.

 

Sick, hospitalized patients may have falsely low or transiently elevated TSH.

Testing Algorithm

See Thyroid Function Ordering Algorithm in Special Instructions.

Analytic Time

Same day/1 day

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Clinical Reference

1. Fatourechi V, Lankarani M, Schryver P, Vanness D, Hall-Long K, Klee G: Factors influencing clinical decisions to initiate thyroxine therapy for patients with mildly increased serum thyrotropin (5.1-10.0 mIU/L). Mayo Clin Proc. 2003 May;78(5):554-560

2. Wilson JD, Foster DW, Kronenburg HM, Larsen PR: Williams Textbook of Endocrinology. 9th ed. Saunders Company; 1998

3. Melmed S, Polonsky KS, Larsen PR, Kronenberg H: Williams Textbook of Endocrinology. 12th ed. Saunders Company; 2011:348-414

4. Heil W, Ehrhardt V: Reference intervals for adults and children. 9th ed. Roche Diagnostics; 2009 Jul;V9.1

5. Freedman DB, Halsall D, Marshall WJ, Ellervik C: Thyroid disorders. In: Rifai N, Horvath AR, Wittwer CT: eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:1572-1616

Method Name

Electrochemiluminescent Immunoassay

Specimen Type

Serum


Advisory Information


This is a standalone test for sensitive thyrotropin (s-TSH; previously known as thyroid-stimulating hormone).

 

If a cascade approach is preferred, order THSCM / Thyroid Function Cascade, Serum, which utilizes a cascaded testing procedure to efficiently evaluate and monitor functional thyroid status. Serum thyrotropin is the first-line test and when the s-TSH result is abnormal, appropriate follow-up tests will automatically be performed.



Specimen Required


Patient Preparation: For 12 hours before specimen collection do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.

Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.6 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 7 days
  Frozen  30 days
  Ambient  7 days

Reference Values

0-5 days: 0.7-15.2 mIU/L

6 days-2 months: 0.7-11.0 mIU/L

3-11 months: 0.7-8.4 mIU/L

1-5 years: 0.7-6.0 mIU/L

6-10 years: 0.6-4.8 mIU/L

11-19 years: 0.5-4.3 mIU/L

≥20 years: 0.3-4.2 mIU/L

 

For SI unit Reference Values, see https://www.mayocliniclabs.com/order-tests/si-unit-conversion.html

Test Classification

This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

84443

LOINC Code Information

Test ID Test Order Name Order LOINC Value
STSH TSH, Sensitive, S 11579-0

 

Result ID Test Result Name Result LOINC Value
STSH TSH, Sensitive, S 11579-0
Mayo Clinic Laboratories | Endocrinology Catalog Additional Information:

mml-endo-thyroid