Test/Investigation
Free thyroxine (fT4)
Site(s) or Laboratory offering Test/Investigation
NNUH, QEH, JPUH
Units
pmol/L
Comments/Precautions
Part of thyroid profile for the investigation of thyroid disorders. Please contact the lab if you suspect assay interference
Sample type
Serum
Turnaround times (TAT) Urgent/Routine/GP or OPD
1 hour / 4 hour / by 8am next day
Reference intervals (adult unless stated)
Adult (> 18 yr) range: 9.0 – 19.1 pmol/L
Paediatric ranges:
5 days – 14 days 13.5 – 41.3 pmol/L
15 days – 29 days 8.7 – 32.5 pmol/L
30 days – < 1 yr 11.4 – 21.9 pmol/L
1 yr – < 19 yr 9.3 – 17.6 pmol/L (n=952)
If UKAS Accredited Test indicate at which site
Y NNUH, QEH
Source
Adult ranges: Abbott Alinity kit insert [G71158R03] Paediatric ranges: The source for the fT4 range for 1 yr – < 19 yr is based on Norfolk population data (evidenced in EPA-CC-628) [the range it refers to is: 9.3 – 17.6 pmol/L (n=952)] Other fT4 paediatric ranges are from: CALIPER (Adeli, K., Higgins, V., Trajcevski, K., White-Al Habeeb, N. (2017). The Canadian laboratory initiative on pediatric reference intervals: A CALIPER white paper. Crit Rev Clin Lab Sci, 54(6):358-413. doi: 10.1080/10408363.2017.1379945. Epub 2017 Oct 11. Erratum in: Crit Rev Clin Lab Sci. 2020 Mar;57(2):145. PMID: 29017389.)