Free Thyroxine Index
Other names: Free T4 Index Test, FTI, FREE T4 INDEX (T7)
What is the Free Thyroxine Index (FTI)?
The free T4 index (FTI) is a blood test used to diagnose thyroid disorders. T4, also called thyroxine, is a thyroid hormone. The test measures how much of it is in your blood to help determine whether your thyroid gland is underactive (hypothyroidism) or overactive (hyperthyroidism).
The Free Thyroxine Index (FTI) is a laboratory test used to assess thyroid function. The FTI provides an estimate of the amount of free, unbound T4 hormone in the bloodstream. This is important because only the unbound T4 is biologically active and can affect various body functions.
Doctors use the FTI to diagnose and monitor thyroid disorders, such as hyperthyroidism and hypothyroidism. Abnormal FTI levels can indicate an overactive or underactive thyroid gland, which can have a significant impact on metabolism, energy levels, and overall health.
Therefore, the Free Thyroxine Index is a valuable tool in assessing thyroid function and guiding appropriate treatment decisions.
If your healthcare provider orders an FTI, it will probably be performed along with other thyroid tests, including thyroid-stimulating hormone (TSH) and triiodothyronine (T3). The results are then analyzed together to help with a diagnosis.
The FTI and other thyroid tests are performed on blood samples, which are fairly quick and simple to obtain and very low risk.
Currently, direct measurement of serum free thyroxine is starting to replace the FTI formula in most clinical situations. Autoantibodies to thyroid hormones can, however, interfere with the assay.
Patients are sent for an FTI and other thyroid tests if they have symptoms that could indicate a thyroid disease, especially in the presence of other risk factors (female gender, age below 40, family history of thyroid disorders).
How is the Free Thyroxine Index calculated?
The FTI is calculated using a formula that involves total thyroxine (T4) and a measurement called the thyroid hormone-binding index (TBI).
FTI = Thyroxine (T4) / Thyroid Binding Capacity
FTI levels in healthy adults:
In healthy individuals, the FTI remains relatively constant and helps compensate for abnormal levels of binding proteins. The normal range for the FTI is typically between 1.2 - 4.9 Units, though specific reference ranges may vary depending on the laboratory and population being tested.
What is the thyroid and how does it relate to T4?
The thyroid is located in the front of your throat and is shaped like a butterfly. Its purpose is to make hormones and regulate several important bodily functions, such as energy use, weight, body temperature, and mood.
In your body, T4 functions in two different forms.
→ One form bonds with a protein to perform certain tasks,
→ and another form doesn't, which allows it to do different jobs.
The FTI test checks only for the "free" form, which is the form not bonded with a protein. It's useful for evaluating thyroid function.
Is the FTI a separate blood test?
The FTI is not itself a separate blood test, but is calculated from the results of the total T4 test and the T3 resin uptake test. Because the FTI is often made inaccurate by medical conditions that change blood protein levels, it is not used very much in clinical medicine today. Instead, the free T4 level is now measured directly.
What does it mean if your Free Thyroxine Index result is too high?
A high Free Thyroxine Index (FTI) typically suggests an overactive thyroid gland or hyperthyroidism. The FTI is a measurement that reflects the availability of free thyroxine (T4) hormones in the bloodstream. T4 is a crucial hormone produced by the thyroid gland, which plays a vital role in regulating metabolism.
When the Free Thyroxine Index is elevated, it indicates an excess of free T4 in the blood. Hyperthyroidism can have various causes, including Graves' disease, toxic nodular goiter, or thyroiditis. Symptoms of hyperthyroidism may include weight loss, rapid heart rate, anxiety, and excessive sweating.
If you receive a high FTI result, it's essential to consult a healthcare provider for further evaluation and diagnosis. They may recommend additional thyroid function tests, such as TSH (Thyroid-Stimulating Hormone) and T3 (Triiodothyronine) measurements, to determine the underlying cause of hyperthyroidism. Treatment options may include medications, radioactive iodine therapy, or surgery, depending on the specific diagnosis.
All Your Lab Results.
One Simple Dashboard.
Import, Track, and Share Your Lab Results Easily
Import, Track, and Share Your Lab Results
Import lab results from multiple providers, track changes over time, customize your reference ranges, and get clear explanations for each result. Everything is stored securely, exportable in one organized file, and shareable with your doctor—or anyone you choose.
Cancel or upgrade anytime
What does it mean if your Free Thyroxine Index result is too low?
A low Free Thyroxine Index (FTI) typically indicates an issue with thyroid function, specifically hypothyroidism, which means an underactive thyroid gland. The FTI is a measure that assesses the availability of free thyroxine (T4) hormones in the bloodstream. T4 is a critical hormone produced by the thyroid gland that plays a key role in regulating metabolism.
When the Free Thyroxine Index is low, it suggests that there is an insufficient amount of free T4 available in the blood. This can lead to a variety of symptoms, including fatigue, weight gain, cold intolerance, and depression. Hypothyroidism can have various causes, including autoimmune thyroiditis (Hashimoto's disease), iodine deficiency, or certain medications.
If you receive a low FTI result, it's essential to consult a healthcare provider for further evaluation and diagnosis. They may recommend additional thyroid function tests and potentially prescribe thyroid hormone replacement therapy to address the underlying hypothyroidism and alleviate symptoms.
Laboratories
Bring All Your Lab Results Together — In One Place
We accept reports from any lab, so you can easily collect and organize all your health information in one secure spot.
Pricing Table
Gather Your Lab History — and Finally Make Sense of It
Finally, Your Lab Results Organized and Clear
Personal plans
$79/ year
Advanced Plan
Access your lab reports, explanations, and tracking tools.
- Import lab results from any provider
- Track all results with visual tools
- Customize your reference ranges
- Export your full lab history anytime
- Share results securely with anyone
- Receive 5 reports entered for you
- Cancel or upgrade anytime
$250/ once
Unlimited Account
Pay once, access everything—no monthly fees, no limits.
- Import lab results from any provider
- Track all results with visual tools
- Customize your reference ranges
- Export your full lab history anytime
- Share results securely with anyone
- Receive 10 reports entered for you
- No subscriptions. No extra fees.
$45/ month
Pro Monthly
Designed for professionals managing their clients' lab reports
- Import lab results from any provider
- Track lab results for multiple clients
- Customize reference ranges per client
- Export lab histories and reports
- Begin with first report entered by us
- Cancel or upgrade anytime
About membership
What's included in a Healthmatters membership
Import Lab Results from Any Source
See Your Health Timeline
Understand What Your Results Mean
Visualize Your Results
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.
What Healthmatters Members Are Saying
Frequently asked questions
Healthmatters is a personal health dashboard that helps you organize and understand your lab results. It collects and displays your medical test data from any lab in one secure, easy-to-use platform.
- Individuals who want to track and understand their health over time.
- Health professionals, such as doctors, nutritionists, and wellness coaches, need to manage and interpret lab data for their clients.
With a Healthmatters account, you can:
- Upload lab reports from any lab
- View your data in interactive graphs, tables, and timelines
- Track trends and monitor changes over time
- Customize your reference ranges
- Export and share your full lab history
- Access your results anytime, from any device
Professionals can also analyze client data more efficiently and save time managing lab reports.
Healthmatters.io personal account provides in-depth research on 10000+ biomarkers, including information and suggestions for test panels such as, but not limited to:
- The GI Effects® Comprehensive Stool Profile,
- GI-MAP,
- The NutrEval FMV®,
- The ION Profile,
- Amino Acids Profile,
- Dried Urine Test for Comprehensive Hormones (DUTCH),
- Organic Acids Test,
- Organix Comprehensive Profile,
- Toxic Metals,
- Complete Blood Count (CBC),
- Metabolic panel,
- Thyroid panel,
- Lipid Panel,
- Urinalysis,
- And many, many more.
You can combine all test reports inside your Healthmatters account and keep them in one place. It gives you an excellent overview of all your health data. Once you retest, you can add new results and compare them.
If you are still determining whether Healthmatters support your lab results, the rule is that if you can test it, you can upload it to Healthmatters.
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.