Pathology Handbook

TSH

Synonyms

Thyroid stimulating hormone

Clinical Indications

TSH secretion is regulated by negative feedback from serum free thyroid hormone levels. The serum TSH response to change in free T4 is logarithmic; a twofold change in free T4 induces inverse 10-100 fold changes in TSH. Thus, this negative amplified feedback as the serum T4 increases or decreases, makes TSH a sensitive marker of thyroid function which can become abnormal before there is a diagnostic change in free T4. 

Part of Profile

Thyroid Function Tests

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Request on ICE

Availability

On request

Specific Criteria

None

There is little value in doing thyroid function tests in acutely ill patients as non-thyroidal illness may result in misleading thyroid function test results.  The test is therefore of limited value in in-patients

It is normally not necessary to repeat TFT's within 4 weeks

Turnaround Time

Same Day (Monday to Friday)

Specimen

Serum in yellow top (SST) tube

Volume

1 ml

Container

 Vacutainer gold top

Collection

No specific collection conditions

Causes for Rejection

Unlabelled or inadequately labelled sample

Reference Range

0.27 to 4.2 mU/L.

Neonates may have levels up to 20 mU/L which decrease to normal by 6 weeks of age.