$5.00
Priced per marker, with baseline labs included. You’ll see your total before you pay.
Thyroid
Free T4 test
Free thyroxine. Biologically active form of T4; key thyroid hormone test alongside TSH.
At a glance
In about 5 days
Most results are ready in about 5 days. Some specialty markers can take up to 21 days.
May have a step to take first. Contact us to ask
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
Your thyroid, the gland in your neck, mainly makes a hormone called T4. Free T4 is the part ready to act, and it’s usually read with TSH, the signal that tells your thyroid how hard to work.
Why it matters for women
Thyroid conditions, which can be caused by the immune system targeting the gland, are much more common in women and can affect your periods, mood, weight and fertility. They can appear after having a baby or in midlife. In pregnancy, your body needs more thyroid hormone, and your baby relies on yours early on.
You might check it if…
- you feel tired, cold or foggy more than usual
- your periods have changed or you’re trying to conceive
- you’re pregnant or recently had a baby
- a TSH result came back outside the normal range
What your result may mean
High Free T4: what it may mean
High free T4 with low TSH may point to an overactive thyroid (hyperthyroidism), such as Graves’ disease, thyroiditis or too much thyroid replacement. Thyroid problems can appear after having a baby, and hCG in early pregnancy can raise free T4 for a short time. Biotin and the blood thinner heparin can sway some tests. You may notice a racing heart, anxiety, heat intolerance, weight loss or lighter periods, and these can be easy to blame on other things. A clinician may add thyroid antibodies to look for the reason.
Low Free T4: what it may mean
Low free T4 with high TSH may point to primary hypothyroidism, an underactive thyroid, such as from Hashimoto’s thyroiditis. If TSH is low or normal, a low free T4 may suggest a pituitary problem instead. Free T4 can also drift lower later in pregnancy on some tests, and serious illness can lower it. You may notice tiredness, weight gain, feeling cold, constipation, dry skin or heavier periods. Because your baby relies on your thyroid hormone early on, a low level in pregnancy can matter.
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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.