$15.00
Priced per marker, with baseline labs included. You’ll see your total before you pay.
Thyroid
Free T4 (direct dialysis) test
Highly accurate Free T4 measurement by equilibrium dialysis.
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
This is one of the most accurate ways to measure free T4, the active part of your thyroid’s main hormone. The lab first separates the free hormone from the hormone attached to proteins, then measures it.
Why it matters for women
Pregnancy and some health conditions can change the proteins that carry thyroid hormone, which can throw off standard free T4 tests. This method is less affected by those changes, so it can help when results don’t fit how you feel or don’t match your TSH. Thyroid conditions are much more common in women.
You might check it if…
- you’re pregnant and your thyroid results seem confusing
- your TSH and free T4 results don’t seem to match
- a doctor wants the most accurate free T4 reading
What your result may mean
High Free T4 (direct dialysis): what it may mean
High free T4 by direct dialysis may support a finding of hyperthyroidism, an overactive thyroid. This method can be most accurate when binding-protein abnormalities make standard free T4 unreliable, such as with inherited protein differences. The blood thinner heparin can falsely raise the result. A racing heart, shakiness or weight loss may go along with an overactive thyroid, and some people may notice very little. Your clinician may compare it with TSH, since the two can tell you more together.
Low Free T4 (direct dialysis): what it may mean
Low free T4 by direct dialysis may support a finding of hypothyroidism, an underactive thyroid. It can be useful in pregnancy, when changing proteins can throw off standard tests, and when other free T4 methods give inconsistent results. Serious illness and some medicines can lower it too. Constipation, tiredness, feeling cold or heavier periods can come with it. Results can take longer than a standard test, and a clinician may read this one with TSH to see whether the thyroid or pituitary may be involved.
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No insurance required · HSA/FSA eligible · No subscription
These notes provide context and do not diagnose a condition. Not yet available in NY, NJ, RI, HI, ND, SD or WV.