Clinical Use:
Background: TSH is secreted by the pituitary gland. It is composed of two subunits called alpha and beta. Other hormones such as LH, FSH and HCG have virtually identical alpha subunits, but the beta subunits are different. These differences are exploited by immunoassay.

The main function of TSH is to regulate the release of T4 and T3 from the thyroid. High levels of these hormones exert a negative feed back effect on the pituitary, inhibiting the release of TSH. Low levels of T4 or T3 act upon the hypothalamus causing it to release thyroid releasing hormone (TRH). This stimulates the pituitary to produce TSH, which in turn causes the release of T4 and T3 from the thyroid. In the normal individual there is a dynamic equilibrium established between the hormones which maintain normality.

TSH is the “Front Line” assay for Thyroid Function Testing in this department. In the absence of a previous clinical history of Thyroid Disease, only the TSH will be measured. Further investigation may be indicated by the TSH result obtained.

Reference Ranges: 0.27 – 4.2 mU/L
Associated Diseases:
Patient Preparation:
Specimen Requirements: Sample Type:

  • Serum is the recommended sample type for this assay, although heparinised plasma may be used.

Sample Identification:

  • Three patient identifiers from
    • Name
    • D.O.B.
    • Address
    • N.H.S. number
    • Unit Number

    should match on the specimen and request form. This check may be performed prior to centrifugation by the Central Sort department.

Turnaround Time: 2 hours
Additional Information:
Referred Test: