Thyroid stimulating hormone (TSH) - serum

Last updated: Wednesday, 31, March, 2004

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Item Process
Specimen

5 mL blood in plain tube.

Method

Immunoassay.

Reference Interval

 0.4-5.0 mIU/L (depends on method).

Application

TSH estimation by a high sensitivity assay is now accepted as the first line test for assessment of thyroid function.

Monitoring of patients on thyroid replacement or suppressive therapy.

Interpretation

TSH has been adopted as the initial test of thyroid function as it is more sensitive than free T4 to alterations of thyroid status in patients with primary thyroid disease.

High levels are found in primary hypothyroidism.

Successful thyroid replacement therapy should be associated with a return of TSH to within the reference interval, however this may take several weeks to achieve.

Suppressed levels are found in hyperthyroidism; very rarely, hyperthyroidism may be due to pituitary overproduction of TSH.

In the treatment of thyroid cancer, TSH should be suppressed, but not to undetectable levels.

In hypopituitarism, levels are usually low but may be within the reference interval.

Reference

Surks MI et al. JAMA 2004; 291(2): 228-238.