Pathology Handbook

Thyroid Function Tests

Synonyms

TFT's

Clinical Indications

Screening for suspected thyroid disease and monitoring treatment for hypo- and hyperthyroidism.

Test Includes

TSH is measured as a first line test followed up with free T4 and free T3  as indicated.  It should be noted that this 'TSH first' strategy can give a false indication of thyroid status in pituitary dysfunction. Therefore, requests for thyroid function where pituitary dysfunction is known or suspected, must be clearly indicated so that appropriate tests can be undertaken. 

Request Form 

Request on ICE: follow on-screen choices to ensure that the appropriate tests are requested.

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

Causes for Rejection

Unlabelled or inadequately labelled sample

Reference Range

Reference ranges only apply without non-thyroidal illness.

TSH levels may be suppressed or slightly raised in patients with acute non-thyroidal illness and tests should be repeated when the patient is not acutely ill.

Age TSH (mU/L) FT4 (pmol/L) FT3 (pmol/L)
Newborn 0.70 - 15.2 11.0 - 32.0 2.7 - 9.7
6 days to 3 months 0.72 - 11.0 11.5 - 28.3 3.0 - 9.3
4 to 12 months 0.73 - 8.35 11.9 - 25.6 3.3 - 8.9
1 to 6 years 0.70 - 6.00 12.3 - 22.8 3.7 - 8.5
7 to 11 years 0.60 - 4.85 12.5 - 21.5 3.9 - 8.0
12 to 20 years 0.50 - 4.30 12.6 - 21.0 3.9 - 7.7
Adults 0.27 - 4.20 12.0 - 22.0 3.1 - 6.8