A patient seated in the chair before a blood draw
In person

Total T4

All the T4 thyroid hormone in your blood, from one blood draw.

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  • 2,000+ lab locations. Find one near you
  • Nothing due at the lab. FSA / HSA accepted
  • Ordered by a licensed clinician

At a glance

Collection
Blood draw
A standard blood draw at the lab.
Preparation
None
Nothing to do ahead of time. Water is fine.
Results
1 to 3 days
Typical turnaround after your visit.
Where
2,000+ lab locations
Nationwide, with nothing due at the lab.

About this test

Total T4 measures all the thyroxine (T4) in your blood, both the part attached to carrier proteins and the small unbound part. T4 is the main hormone the thyroid releases. Total T4 is read with TSH to check thyroid function, and Free T4 is the more common choice today. No fasting needed.

For adults 18 and older. Test availability varies by lab location.

Who should take this test?

This test is for adults following up on a TSH result or checking thyroid levels with a healthcare provider, including people who have tracked total T4. Commonly related symptoms include:

Body

  • Tiredness
  • Feeling cold or too warm

Weight

  • Unexplained weight change

Hair

  • Hair thinning

Skin

  • Dry skin

Neck / thyroid

  • Swelling in the neck

Ask about this test

Not sure this is the right test?

AI-generated. For information only, not medical advice. Call 911 for an emergency.

What does this test measure?

Your result shows the total amount of T4 in your blood, which, read with TSH, can help a healthcare provider understand whether your thyroid may be underactive or overactive.

Total T4
Total T4 measures both the bound and unbound forms of thyroxine, the main thyroid hormone. Changes in the proteins that carry T4, for example with pregnancy or estrogen, can shift total T4 even when thyroid function is steady, which is why free T4 is often read too.
Why it’s measured: Bound plus unbound T4, read with TSH and free T4 when protein levels may shift.

How it works

  1. Step 1

    Order online

    Check out here. A licensed clinician in your state reviews your order and sends it to the lab.

  2. Step 2

    Visit a lab

    Bring a photo ID to any of 2,000+ lab locations. No fasting needed, and nothing is due at the lab.

  3. Step 3

    Get your results

    Results post to your account, usually in 1 to 3 days, each number next to the lab’s reference range.

Find a lab near you

Choose from 2,000+ lab locations nationwide. Your order works at any of them.

What your results tell you

Total T4 is reported in micrograms per deciliter (mcg/dL) and shown next to the lab’s reference range for comparison.

  • Your number next to the lab’s reference range
  • Explained in plain language
  • A licensed clinician reviews your order and, if appropriate, orders the test.
  • A lab report you can download and share

Total T4 is read with TSH and your symptoms. A healthcare provider can explain your result and whether Free T4 would add context.

Total T4 or Free T4?

Two ways to measure the same hormone.

Total T4

All the T4 in your blood, bound and unbound.

Measures
Bound and unbound T4 together
Carrier proteins
Can shift when their levels change
Mainly used for
Thyroid checks, read with TSH

Clinical-grade testing, from the comfort of home.

From the lab to your report, every step of our process meets the gold standard in medical testing.

  • CLIA-certified labs

    Every lab we partner with is certified under the Clinical Laboratory Improvement Amendments, meeting both state and federal standards with regular independent inspections.

  • We protect your health data

    We protect your health data with encryption and do not sell it. Some results must be reported to public health authorities by law. See our Privacy Notice.

  • Rigorous quality assurance

    All partner labs run regular internal quality checks, participate in proficiency testing, and comply with federal and state lab regulations.

  • Clinician-reviewed reports

    Results are reviewed by an independent, licensed clinician.

Questions

Common questions.

Anything else, our care team answers by phone, text, or email.

Most T4 travels attached to carrier proteins. If the level of those proteins goes up or down, total T4 follows, even when thyroid activity stays the same. Free T4 measures the unbound portion, which is less affected by these proteins.

TSH is the pituitary’s signal to the thyroid. It tends to rise when thyroid hormone is low and fall when it is high. Reading T4 with TSH helps a healthcare provider see whether the two line up and whether the thyroid may be underactive or overactive.

Total T4 doesn’t separate bound and unbound hormone, so it can be harder to read when carrier protein levels change. It also doesn’t show the cause of a high or low result. A healthcare provider may suggest Free T4, TSH, or antibody tests to learn more.

Lab tests are informational and don’t diagnose conditions on their own. Available to adults 18 and older; test availability varies by lab location. A licensed clinician reviews your order and, if appropriate, orders the test. All testing is performed at CLIA-certified laboratories. Not for emergencies: if you think you may be having a medical emergency, call 911.