Metabolic Health

Free Thyroxine

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

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

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 

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)

10 000+ happy clients
100% satisfaction
★ ★ ★ ★ ★ customer support

Understand blood, stool, and urine medical results from all your laboratories.

Get Started With Our Personal Plan

Advanced Plan

  • ✓ Yearly subscription
  • ✓ Five free uploads
  • ✓ Cancel anytime
  • ✓ Instant interpretations
  • ✓ Use the free self-upload form
  • ✓ 3000+ biomarkers explained
  • ✓ Nutrition Recommendations
  • ✓ Dedicated support
  • ✓ Yearly subscription
  • ✓ Five free uploads
  • ✓ Cancel anytime
$79 per year
  • ✓ Instant interpretations
  • ✓ Use the free self-upload form
  • ✓ 3000+ biomarkers explained
  • ✓ Nutrition Recommendations
  • ✓ Dedicated support

Unlimited Plan

  • ✓ No subscription
  • ✓ Ten free uploads
  • ✓ Unlimited access
  • ✓ Instant interpretations
  • ✓ Use the free self-upload form
  • ✓ 3000+ biomarkers explained
  • ✓ Nutrition Recommendations
  • ✓ Dedicated support
  • ✓ No subscription
  • ✓ Ten free uploads
  • ✓ Unlimited access
$250 full version

Are You a Health Professional?

Get started with our professional plan

Welcome to Healthmatters Pro.

Save time on interpreting lab results with the largest database of biomarkers online. In-depth research on any test at your fingertips, all stored and tracked in one place. Learn more

Pro Plan

for health professionals

  • ✓ Track multiple clients results
  • ✓ No setup fees
  • ✓ No hidden costs
  • ✓ Cancel anytime
  • ✓ Instant interpretations
  • ✓ Use the free template forms
  • ✓ 3000+ biomarkers explained
  • ✓ Additional team member $25
  • ✓ Personal training and support

$45 per month

Use promo code to save 10% off any plan.


We implement proven measures to keep your data safe.

At HealthMatters, we're committed to maintaining the security and confidentiality of your personal information. We've put industry-leading security standards in place to help protect against the loss, misuse, or alteration of the information under our control. We use procedural, physical, and electronic security methods designed to prevent unauthorized people from getting access to this information. Our internal code of conduct adds additional privacy protection. All data is backed up multiple times a day and encrypted using SSL certificates. See our Privacy Policy for more details.

×

Understand Your Lab Result Now

  • Instant interpretation
  • 3000+ biomarkers explained
  • Science-based recommendations
  • Online support
  • Secure and private portal

Get 10% off with promocode: