Free T4 (Thyroxine, Free)
CPT 84439 measures free thyroxine (Free T4), the active form of thyroid hormone circulating in your blood. It is usually ordered alongside TSH (CPT 84443) for thyroid evaluation, and over 3.5 million Medicare beneficiaries received this test in 2023. Providers charge an average of $83.35, but Medicare pays only $10 to $14. The key question for your bill: if your TSH was normal, did you actually need the Free T4? Ordering both when TSH alone would suffice adds $83 to your bill without changing your clinical picture.
CPT 84439 at a Glance
- Medicare CLFS rate: ~$10 to $14
- Average provider charge: $83.35
- Markup: 6x to 8x over Medicare rate
- Direct-to-consumer price: $15 to $30
- Test type: Single analyte (Free Thyroxine)
- Beneficiaries (2023): 3.5 million
- Fee schedule: Clinical Laboratory (CLFS)
- Rate type: National (no geographic adjustment)
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How Lab Pricing Works (Clinical Laboratory Fee Schedule)
Unlike physician services that use RVUs and geographic adjustments, lab tests are priced under the Medicare Clinical Laboratory Fee Schedule (CLFS). The CLFS sets a single national rate for each lab test. There are no RVU components and no geographic cost adjustments. Medicare pays the same rate for a Free T4 test regardless of where the lab is located. The CLFS rate for CPT 84439 is approximately $10 to $14.
| Metric | Value |
|---|---|
| Medicare CLFS Rate | ~$10 to $14 |
| Average Provider Charge | $83.35 |
| Markup Ratio | 6x to 8x |
| Pricing Method | National rate (CLFS), no geographic variation |
Lab tests are priced under the Clinical Laboratory Fee Schedule, not the Physician Fee Schedule. Medicare lab rates are set nationally and do not vary by geographic location.
What Does a Free T4 Test Measure?
Free T4 measures the unbound, active form of thyroxine in your blood. Unlike total T4 (which includes protein-bound hormone), Free T4 reflects the amount of thyroid hormone actually available for your body to use.
Result Ranges (typical)
- Below 0.8 ng/dL: Low (possible hypothyroidism)
- 0.8 to 1.8 ng/dL: Normal range
- Above 1.8 ng/dL: High (possible hyperthyroidism)
- Ranges vary slightly by lab
When Free T4 Is Clinically Useful
- TSH is abnormal and further evaluation is needed
- Suspected pituitary disorder (central hypothyroidism)
- Evaluating new thyroid symptoms (weight changes, fatigue, tremor)
- Adjusting thyroid medication dosage
- Monitoring patients on amiodarone or lithium
Where to Get a Free T4 Test for Less
Like most lab tests, the price for Free T4 varies dramatically depending on where you go. Here are your options, ranked from cheapest to most expensive:
Direct-to-Consumer Labs: $15 to $30
Services like Quest Diagnostics (walk-in), LabCorp, Ulta Lab Tests, Jason Health, and Walk-In Lab allow you to order a Free T4 test without a doctor's order in most states. Many offer thyroid panels (TSH + Free T4) for $30 to $50, which is cheaper than the Free T4 alone at a hospital lab.
Independent Labs (with doctor's order): $20 to $40
If your doctor orders the test, ask for the order to be sent to an independent lab (Quest or LabCorp) rather than the hospital's in-house lab. The same Free T4 assay at an independent lab costs a fraction of the hospital price.
Hospital Outpatient Labs: $50 to $130+
Hospital labs are the most expensive option. The $83.35 national average charge reflects typical hospital pricing. If your doctor is part of a hospital system, the lab order may automatically route to the hospital lab. Ask if you can use an independent lab instead.
What Insured Patients Actually Pay for a Free T4 Test
Most insurers cover Free T4 testing when medically indicated. What you owe depends on your plan design:
| Your Situation | What You Likely Pay | How It Works |
|---|---|---|
| Copay plan (deductible met or N/A) | $0 to $10 | Many plans cover lab work at 100% after deductible |
| Coinsurance plan (deductible met) | $1 to $5 | 20% of negotiated rate ($5 to $25) |
| High-deductible plan (deductible NOT met) | $8 to $25 | Full negotiated rate applied to your deductible |
| Medicare Part B | $0 | Medicare covers clinical lab tests at 100% (no coinsurance) |
Common Billing Problems with CPT 84439
Free T4 ordered routinely when TSH alone was sufficient
The most common billing issue with Free T4 is unnecessary ordering. For routine thyroid screening in asymptomatic patients, TSH alone is the recommended first-line test. Free T4 should be ordered when TSH is abnormal or when there is a clinical reason to check both. If your TSH came back normal and you were also charged for a Free T4, the second test may not have been necessary. At $83 per test, routine ordering of both tests without clinical indication adds up quickly.
Non-reflex ordering (running both tests regardless)
Some labs offer "reflex" thyroid testing: they run TSH first, and only run Free T4 if the TSH is abnormal. This is the cost-effective approach. Other labs (and some doctors' standing orders) run both TSH and Free T4 on every sample regardless of the TSH result. If your TSH was normal, ask whether the Free T4 was part of an automatic order or whether it was specifically requested. Switching to reflex ordering can save $83 per blood draw when TSH is normal.
Free T4 vs Total T4 confusion
CPT 84439 is Free T4 (the active, unbound form). CPT 84436 is Total T4 (includes both bound and unbound hormone). Free T4 is the preferred test in most clinical situations because it is not affected by protein levels that can skew Total T4 results. If you see both a Free T4 and Total T4 on the same bill, one of them is likely unnecessary. Confirm with your doctor which test was actually needed.
Related Thyroid Test Codes
| Code | Description | Medicare CLFS | Avg. Charge |
|---|---|---|---|
| 84443 | TSH (Thyroid Stimulating Hormone) | ~$14-$18 | $83.00 |
| 84439 | Free T4 (Thyroxine, Free) | ~$10-$14 | $83.35 |
| 84436 | Total T4 (Thyroxine, Total) | ~$8-$12 | $65.00 |
| 84480 | Free T3 (Triiodothyronine, Free) | ~$14-$18 | $90.00 |
Frequently Asked Questions
How much does a Free T4 test cost without insurance?
Without insurance, a Free T4 test (CPT 84439) costs $40 to $130 at most hospitals and clinics, with the national average charge at $83.35. Direct-to-consumer labs like Quest, LabCorp, Ulta Lab Tests, and Jason Health offer the same test for $15 to $30 without a doctor's order in most states. Medicare pays approximately $10 to $14.
Do I need both TSH and Free T4 tested?
Not always. For routine thyroid screening, TSH alone is usually the recommended first-line test. Free T4 adds the most value when your TSH is abnormal, when evaluating pituitary disorders, or when adjusting thyroid medication dosage. If your TSH is normal and you have no thyroid symptoms, a Free T4 may not be necessary and adds about $83 to your bill at average provider charges.
What is reflex testing for thyroid labs?
Reflex testing means the lab automatically runs a Free T4 only if your TSH result comes back abnormal. This is the most cost-effective approach because it avoids an unnecessary $83 charge when TSH is normal. However, some labs and doctors' standing orders run both TSH and Free T4 on every sample regardless. Ask your doctor whether they use reflex ordering. If not, you could save $83 per blood draw when your TSH is within range.
Does Medicare cover Free T4 testing at 100%?
Yes. Medicare Part B covers clinical laboratory tests, including Free T4 (CPT 84439), at 100% of the Clinical Laboratory Fee Schedule rate. There is no coinsurance or copay for lab tests under Medicare. You pay $0 out of pocket, as long as the test is medically necessary and ordered by your treating physician.
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