T4, free
- Test Name:
- T4, free
- Synonyms:
-
Free thyroxine
FT4
-
Ordering Information:
- Laboratory staff: If "T4" is written alone, order "T4, free" (FT4)
- Collection Device/Tube Type:
-
1. EDM Base Lab: 5 mL blood - GOLD SST (gel)
2. CGY DSC: 4.5 mL blood - MINT LIHEP PST (gel)
3. NOTE: The preferred tube type at each testing site is acceptable at the alternate site
- Submission Requirements:
- 1 mL serum or lithium heparin
- Frequency of Testing:
-
Daily
- Reference Range:
-
Note: For interpretation of the test results in pregnancy, refer to the care pathway at Thyroid Function in PregnancyAge
FT4 (pmol/L)
0 to < 15 days
13.5 – 50.0
15 days to < 30 days
8.7 – 32.5
≥ 30 days
10.0 – 25.0
- Comments:
-
Free T4 is ordered by the resulting location when progressive Thyroid stimulating hormone (TSH) testing is ordered and the TSH result is < 0.10 mIU/L
For testing referred to Edmonton Base Lab:
• Serum is the preferred specimen type for Free T4 measurement. It has been noted that Free T4 results are approximately 20% higher in plasma compared to serum. A comment reflecting this positive bias will be appended to Free T4 results from plasma samples, as the free T4 reference range was established from serum samples. Refer to: Update to thyroid hormone reference intervals and to the progressive TSH algorithm (Lab Bulletin, 13 June 2022) - Last Reviewed:
- 26 March 2025
