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PTD - 293

Test Directory -  Free T3



Clinical Indications

Free T3 levels are useful in the differential diagnosis of hyperthyroidism and non-thyroidal illness; TSH levels may be suppressed in both conditions with normal or raised free T4. Free T3 is not helpful and may be misleading in diagnosis of hypothyroidsim. Free T3 may also be misleading in monitoring T3 replacement because of wide variations that depend on the interval between dose and sampling.

Patients on anti-thyroid treatment may require free T3 levels to identify persistent drug treatment thyrotoxicosis due to isolated T3 excess. 

Part of Profile

Thyroid Function Tests

Request Form 

Combined Pathology Blood form (Yellow/Black or Blue for GP's)


On request. Free T3 is automatically measured if TSH is suppressed.

Specific Criteria

Samples referred to Basildon Hospital for Free T3 analysis from other Hospitals should be packaged in accordance with our transportation policy and will be assumed to have met the specific criteria of the referring laboratory.

Patient Preparation


None required.

Turnaround Time

Same Day




0.5 ml


Yellow top (SST) tube or

Paediatric orange top (lithium-heparin)

Causes for Rejection

Unlabelled sample

Reference Ranges



Free T3 (pmol/L)



0 to 5 days

2.7 - 9.7



6 days to 3 months

3.0 - 9.3



4 months to 1 year

3.3 - 8.9



1 to 6 years

3.7 - 8.5



7 to 11 years

3.9 - 8.0


12 to 18 years

3.9 - 7.7


Over 18 years

3.1 - 6.8


Reference: Roche method insert         


Interpretive comment will be provided based on clinical information and the results.

Lab Handling

Processing: Analysed from primary tube and stored at 4C in the cold room (CB23)


Version 1.1 / October 2014                                                                                                      Approved by: Consultant Biochemist