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PTD - 294

Test Directory -  Free T4



Clinical Indications

Free T4 levels are required for definitive assessment of thyroid status when TSH is abnormal and if pituitary dysfunction is suspected.
During long-term replacement or suppressive therapy with thyroxine, TSH is the best index of appropriate dose (unless treatment of hypothyroidism due to pituitary or hypothalamic disease). Free T4 levels are also required in early treatment of hyperthyroid disease, since TSH levels may remain suppressed for several months after normalisation of free T4.

Part of Profile

Thyroid Function Tests

Request Form 

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


On request. Free T4 is automatically measured if TSH level is abnormal or in suspected pituitary dysfunction.

Specific Criteria


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 T4 (pmol/L)



0 to 5 days

11.0 - 32.0



6 days to 3 months

11.5 - 28.3



4 months to 1 year

11.9 - 25.6



1 to 6 years

12.3 - 22.8



7 to 11 years

12.5 - 21.5


12 to 18 years

12.6 - 21.0


Over 18 years

12.0 - 22.0


Reference: Roche method insert              

Interpretation 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 1.0 / July 2014                                                                                                            Approved by: Consultant Biochemist