Free T4 Test Cost and Medicare Coverage (CPT 84439)
Also called: FT4 · free thyroxine · T4 free — all the same test, CPT 84439 (related code: 84436).
National policy — the same Medicare rules apply in every state what's this?
This test is governed by a National Coverage Determination (NCD) — a rule issued by CMS, the federal agency that runs Medicare. It spells out which diagnoses justify the test and any frequency limits, it applies identically in all 50 states, and no regional contractor can override it. What you read on this page is the rule everywhere.
- Does Medicare cover it?
- Yes — with frequency limits
- You pay if covered
- $0 — no deductible, no coinsurance
- Medicare pays the lab
- $9.02
- Information verified
- 2026-09-17
Buy it yourself — what you'd really pay
| Where | Test price | Fee | Total |
|---|---|---|---|
| Jason Health jasonhealth.com | $10 | $18 one fee per order — covers every test on it | $28 |
| Ulta Lab Tests ultalabtests.com Partner link — we earn a commission if you order. No extra cost to you. | $25.95 | $12.95 draw fee — one per order, covers every test on it | $38.90 |
| Personalabs personalabs.com · price includes the draw; not a partner — we earn nothing from this row | $77 | — | $77 |
Disclosure: the Ulta Lab Tests link above is a partner link. If you order through it, ClaraCover earns a commission. It costs you nothing extra, and it never changes what we tell you about Medicare coverage.
The short answer
Yes — under the same national thyroid policy as the TSH, with the same rhythm rule. The free T4 is the natural second step of a thyroid workup, and Medicare’s national policy (NCD 190.22 — the same in every state) covers it for diagnosing thyroid problems, monitoring treatment, and evaluating a long list of symptoms. The rule to know is the frequency: for patients whose thyroid treatment is stable, covered testing runs up to twice a year — more only when a dose changed or symptoms returned. (What free T4 measures and what a high or low result can mean.)
When Medicare DOES cover it
- Following up an abnormal TSH — the classic pairing: TSH flags a problem, free T4 sizes it
- Diagnosing thyroid disease — confirming an overactive or underactive thyroid
- Monitoring treatment — hormone replacement, anti-thyroid therapy, goiter, nodules, and thyroid cancer follow-up
- Working up symptoms — the national list is broad: fatigue, unexplained depression, arrhythmias, high cholesterol, and many other signs the thyroid can produce
When Medicare does NOT cover it
- More than twice a year for a stable patient without a documented change in dose or symptoms
- Pure routine screening with nothing thyroid-related in the picture
What you pay if it IS covered: $0
Covered lab tests cost Medicare patients nothing — no deductible, no 20% coinsurance. Medicare pays the lab $9.02 for a free T4, and you owe zero.
What it costs to buy yourself
Here’s a retail quirk: Quest’s and Labcorp’s consumer sites don’t sell the free T4 by itself — they bundle it into thyroid panels (Labcorp’s standard panel runs $89). Jason Health sells it alone for $10 (jasonhealth.com — add their flat $18 lab-collection fee per order; pairing it with their $10 TSH on one order costs $38 all-in for both). Same certified labs, same blood draw.
What counts as a “normal” free T4 result
Start with the range printed on your own report. There is no single published standard to compare it with. Unlike blood sugar or cholesterol, no major medical body publishes an agreed cut-off for this test, so each laboratory sets its own from its own sample of people on its own equipment. Two labs can report the same blood differently.
Free T4 is also rarely read alone. It is interpreted together with TSH, and it is the pattern across the pair — not either number by itself — that tells your doctor what your thyroid is doing.
(Where lab ranges and “optimal” ranges come from, and who decides.)
This page can tell you where those numbers came from. It cannot tell you what yours means — that reading belongs to your doctor, alongside your history and your other results.
Quick questions people ask
What is free T4? T4 (thyroxine) is the main hormone your thyroid makes. Most of it rides through your blood attached to proteins; “free” T4 is the small unattached fraction your body can actually use — which is why it’s the better measure of what your thyroid is really delivering. On lab orders you’ll see it written FT4, T4 Free, or free thyroxine; on billing paperwork it’s CPT code 84439.
How is free T4 different from TSH? The TSH is the thermostat signal — your brain’s message telling the thyroid to work harder or ease off. Free T4 is the temperature — the hormone actually circulating. Doctors usually start with the TSH and add free T4 when the TSH comes back abnormal or treatment is being tuned. Two tests, two codes, two lines on the bill.
Do you have to fast for a free T4 test? No fasting needed. As with the TSH, if you take thyroid medication, many doctors prefer the draw before your morning dose — ask how yours wants it done. See our guide to fasting before blood work.
Sources and data dates
Medicare payment amount: CMS Clinical Laboratory Fee Schedule, 2026 Q3 file (national rate). Coverage rules: CMS Medicare Coverage Database, NCD 190.22 (Thyroid Testing) — a national policy, identical in every state. Consumer prices and catalogs checked September 2026. Information current as of the date shown above; coverage is always determined by Medicare when your claim is processed.
ClaraCover provides information, not medical, billing, or insurance advice. Talk to your doctor about what tests you need.
Covered diagnoses for CPT 84439
Medicare's national rule for this test, NCD 190.22, Thyroid Testing, comes with a list of 1,404 ICD-10 diagnosis codes that support it (CMS's laboratory code list, updated every quarter). In plain English, the covered situations are the ones described on this page. A claim whose diagnosis is on the list pays; a claim without one is denied as not medically necessary unless another provision of the rule applies.
Billing office? The full list, a batch check, and no daily limit are what we are building for you: tell us you want it. For why lab tests are the one place Medicare gives a straight answer, see what "reasonable and necessary" means.