Total T3 Test
A Total T3 test measures total triiodothyronine, counting both the bound and unbound forms of this thyroid hormone. Clinicians sometimes use it to help round out an evaluation of thyroid activity.
About this test
Triiodothyronine, or T3, is one of the hormones connected to thyroid activity, and it is more metabolically active than T4. In the blood, most T3 travels attached to carrier proteins, while a smaller portion circulates unbound.
The test is performed with a routine blood draw at a patient service center. A phlebotomist collects a sample from a vein in the arm and sends it to the laboratory.
Who might consider this test?
- People who order a total T3 test are often working with a clinician who wants an additional angle on thyroid activity, sometimes alongside TSH and T4.
Test details
| Quest code | 859 |
|---|---|
| Methodology | Immunoassay |
| Sample type | 1 mL serum |
| Collection | Quest patient service center |
Related tests and panels
Quest resources
Additional details
What total means here
The word total is the key to this test. Rather than isolating the small unbound portion of T3, it counts the whole amount present in the blood — both the hormone bound to carrier proteins and the free fraction. The result reflects the full circulating pool of triiodothyronine rather than just the part immediately available to tissues.
That broader scope is useful in some situations, but it also means the reading can move when carrier proteins move, which is something a clinician keeps in mind.
Why carrier proteins matter to the result
Because total T3 includes hormone that is bound, anything that raises or lowers carrier-protein levels can nudge the number even when the thyroid's activity has not changed. This is one of the main reasons a clinician reads total T3 alongside other markers rather than on its own, using the surrounding context to make sense of what the value is reflecting.
What to expect and how results are used
Collection is simple: a phlebotomist draws a small sample from a vein in the arm during a brief visit at a patient service center, and the sample goes to the laboratory. Results are posted to the account when they are ready. From there, a clinician interprets total T3 in the context of symptoms, history, and companion markers such as TSH and T4. Because the total measurement can be swayed by carrier proteins, that surrounding context is especially important, and the report is best viewed as a starting point for a conversation rather than a standalone answer.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does the Total T3 test measure?
It measures the total amount of triiodothyronine in the blood, including both the portion bound to carrier proteins and the portion that is unbound.
How is total T3 different from free T3?
Total T3 counts both bound and unbound hormone. Free T3 counts only the unbound portion, which is less affected by changes in carrier proteins. The choice depends on what a clinician is looking into.
How is the sample collected?
With a standard blood draw at a patient service center. A phlebotomist takes a small sample from a vein in the arm and sends it to the laboratory for analysis.
Can other things affect a total T3 result?
Because total T3 includes hormone bound to carrier proteins, factors that shift those proteins can influence the reading. This is one reason clinicians interpret it alongside other markers.
Is total T3 ordered on its own?
It is often part of a broader look at thyroid activity, ordered together with markers such as TSH and T4 so a clinician can see how the results relate.
What does a T3 Total test cost without insurance?
$45. Celio Health's price is a flat cash price and insurance is never billed: the required physician's order is included.