$9.00
Priced per marker, with baseline labs included. You’ll see your total before you pay.
Thyroid
Free T3 test
Free triiodothyronine. Biologically active thyroid hormone available to tissues.
At a glance
In about 5 days
Most results are ready in about 5 days. Some specialty markers can take up to 21 days.
Check before your draw
This marker has no preparation tag, but it can still need preparation. Contact us before your draw if you’re not sure.
Walk in at Quest
Your lab order arrives by email. Most Quest locations take walk-ins, so bring it with a photo ID.
What it measures
Free T3 is the part of T3, your most active thyroid hormone, that isn’t attached to proteins and is ready to act. It helps set your energy, heart rate and body temperature.
Why it matters for women
Thyroid conditions are much more common in women. Free T3 is most useful when checking for an overactive thyroid, such as Graves’ disease, and can sometimes be high while free T4 is still normal. For an underactive thyroid, TSH, the main thyroid screening test, and free T4 usually tell more.
You might check it if…
- your heart races or your hands shake for no clear reason
- you’ve lost weight without trying
- a past TSH result came back low
- a doctor is checking for an overactive thyroid
What your result may mean
High Free T3: what it may mean
High free T3 may point to an overactive thyroid (hyperthyroidism), from Graves’ disease, thyroiditis, too much thyroid replacement or T3 toxicosis, when free T3 can be high while free T4 stays normal. A thyroid flare after having a baby (postpartum thyroiditis) can push it up as well. A racing heart, sweating, shakiness, weight loss or lighter periods can appear. Biotin supplements can interfere with some free T3 tests, so a clinician may ask about them and check TSH.
Low Free T3: what it may mean
Low free T3 may suggest an underactive thyroid (hypothyroidism), poor T4-to-T3 conversion, or non-thyroidal illness syndrome, when serious illness can lower T3 even though the thyroid is healthy. Fasting and very strict dieting can bring it down too. You may notice tiredness, feeling cold, dry skin or constipation. Because free T3 can stay normal for a while in an underactive thyroid, TSH and free T4 can tell more. A low value during an illness may recover with time.
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These notes provide context and do not diagnose a condition. Not yet available in NY, NJ, RI, HI, ND, SD or WV.