fT4 in Serum

Free T4 is the circulating thyroid hormone reservoir that must be converted to become active.
Also known as:
Free Thyroxine
S-fT4
Free T4
.

fT4 ranges

Interpret your result
"Normal" lab range for fT4 is between 0.93 and 1.7 ng/dL:
0.93
1.7
According to Peter Attia, fT4 should be between 0.93 and 1.7 ng/dL:
0.93
1.7
According to OptimalDX, fT4 should be between 1 and 1.5 ng/dL:
1
1.5
According to Rupa Health, fT4 should be between 1 and 1.7 ng/dL:
1
1.7
Optimal thyroid health was associated with fT4 between 0.99 and 1.58 ng/dL:
0.99
1.58
Reduced all-cause mortality was associated with fT4 between 0.98 and 1.13 ng/dL:
0.98
1.13
Optimal range
Optimal range for fT4 appears to be between 0.97 and 1.4 ng/dL:
0.4
0.97
1.4
1.7
3.5

Enter you value above to interpret your result.

100% free and private. No data will leave your computer.

Images:

fT4 on all-cause mortality

fT4 on all-cause mortality

Values associated with percentiles were calculated from table S3b in supplement-1.
134,346 participants
FT4 decrease and then increase during aging

FT4 decrease and then increase during aging

Chinese population with sufficient iodine intake

Get the Full Picture of Your Thyroid Function

Comprehensive assessment of thyroid function blood tests with HPT axis visualizations designed to detect thyroid-related dysfunction early.

View Full Analysis

100% free and private. Enter only the values you have.

About the site author

My personal mission is to extend human lifespan by collectively adding 1 million years to people's lives.

That’s why I made this site 100% free, no sign-up, no email. Just instant results.

Zsolt Szabo
Zsolt Szabo
Precision Health Consultant for Longevity Clinics, Biohacker, and Software Engineer

Please send me relevant research and feedback.

Any feedback is welcome at .
I am particularly interested in research on biomarkers associated with all-cause mortality and on defining optimal reference ranges.