Free Thyroxine

Serum

Optimal Result: 0.6 - 1.2 ng/dL, or 7.72 - 15.45 pmol/L.

Thyroid Panel

From Healthmatters.io Team

Lab Results Explained and Tracked

Thyroxine (sometime called T4) is a hormone produced by the thyroid gland. The term “free thyroxine” means measured thyroxine that is not bound to proteins in the blood. Thyroxine is only one-tenth as potent as triiodothyronine (T3). That being said, thyroxine acts on almost every cell in the body, helping to setting the metabolic tone of cells. Thyroxine is important for growth and development, especially in fetuses, neonates, and children. The thyroid gland produces and stores thyroxine until it is needed for release. Thyroid-stimulating hormone, also known as TSH or thyrotropin, is produced in the pituitary gland. TSH stimulates the thyroid gland to produce and release of T4. Greater than 99% of thyroxine is bound to serum proteins, but the portion that is not, free thyroxine, is the biologically active portion. In most cases, free thyroxine (also known as free T4) is good indicator of thyroid function, along with TSH and other measures. Free thyroxine is often more useful than total thyroxine in assessing thyroid function.

Normal Ranges for Free T4:

1-23 Months 0.9-1.4 ng/dL

2-12 Years 0.9-1.4 ng/dL

13-20 Years 0.8-1.4 ng/dL

>20 Years 0.8-1.8 ng/dL

Sources:

http://www.ncbi.nlm.nih.gov/books/NBK285568/

http://www.uptodate.com/contents/laboratory-assessment-of-thyroid-function

http://www.ncbi.nlm.nih.gov/pubmed/12625976

http://www.questdiagnostics.com/testcenter/TestDetail.action?ntc=866

http://dx.doi.org/10.1001/jama.1990.03440110095035

http://www.uptodate.com/contents/thyroid-function-in-nonthyroidal-illness

http://www.ncbi.nlm.nih.gov/pubmed?term=7920008

http://www.ncbi.nlm.nih.gov/pubmed/6687730

http://www.uptodate.com/contents/overview-of-thyroid-disease-in-pregnancy

http://www.uptodate.com/contents/diagnosis-of-and-screening-for-hypothyroidism-in-nonpregnant-adults

https://www.uptodate.com/contents/diagnosis-of-hyperthyroidism

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What does it mean if your Free Thyroxine result is too high?

Elevated free thyroxine levels may indicate hyperthyroidism, thyroid hormone resistance syndrome, or thyroxine toxicosis. Elevated free thyroxine may cause symptoms of hyperthyroidism including excessive appetite, anxiety, heart palpitations, sweating, shortness of breath, weight loss, and intolerance to heat.

Some specific causes of high free thyroxine are:

- Hyperthyroidism

- Euthyroid hyperthyroxinemia

- TSH-mediated hyperthyroidism

- Acute thyroiditis

- Pregnancy

- Familial dysalbuminemic hyperthyroxinemia

- Medications (e.g. estrogens, tamoxifen, opioids)

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What does it mean if your Free Thyroxine result is too low?

Decreased free thyroxine levels in the serum usually indicate hypothyroidism or chronic or subacute thyroiditis. Abnormally low thyroxine may cause symptoms of hypothyroidism including weakness and fatigue, cold intolerance, shortness of breath, weight gain, constipation, cognitive problems, dry skin, hoarseness, and swelling (edema).

Some specific causes of low free thyroxine are:

- Hypothyroidism

- Chronic thyroiditis

- Subacute thyroiditis

- Nephrosis

- Congenital thyroid agenesis, dysgenesis, or defects in hormone synthesis

- Synthetic T3 treatment

- Medications anabolic steroids such as glucocorticoids, phenytoin, carbamazepine, phenobarbital

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Free Thyroxine

All Your Lab Results. One Simple Dashboard.

What does it mean if your Free Thyroxine result is too high?

All Your Lab Results. One Simple Dashboard.

Import, Track, and Share Your Lab Results Easily

Import, Track, and Share Your Lab Results

What does it mean if your Free Thyroxine result is too low?

Article Review & Sources

Bring All Your Lab Results Together — In One Place

Gather Your Lab History — and Finally Make Sense of It

Finally, Your Lab Results Organized and Clear

Advanced Plan

Unlimited Account

Pro Monthly

What's included in a Healthmatters membership

Import Lab Results from Any Source

See Your Health Timeline

Understand What Your Results Mean

Enter Your Lab Reports Yourself — Always Free Enter Your Lab Reports — Always Free

Visualize Your Results

Export Your Complete Lab History in a Single File Export Your Complete Lab History

Comprehensive Data Entry Service for Your Reports Data Entry Service for Your Reports

Securely Share With Anyone You Trust

Let Your Lab Results Tell the Full Story

Once your results are in one place, see the bigger picture — track trends over time, compare data side by side, export your full history, and share securely with anyone you trust.

Bring all your results together to compare, track progress, export your history, and share securely.

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All Your Lab Results.
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