Lab & pathology
84439 — Thyroxine; free
A blood test measuring the level of free (unbound) thyroxine hormone, the active form of the thyroid hormone T4, to evaluate thyroid function.
- Typical setting: Hospital lab, reference lab, doctor's office
- National avg charge (illustrative): $10–$22 Medicare allowed (CMS CLFS); $15–$60 commercial; varies by region
- Most-disputed reason: Billing 84439 (free T4) alongside 84436 (total T4) when both were not separately ordered and justified — payers may deny one as duplicative
What it means
What 84439 actually means
A blood test measuring the level of free (unbound) thyroxine hormone, the active form of the thyroid hormone T4, to evaluate thyroid function. It is commonly ordered alongside TSH to diagnose hypothyroidism, hyperthyroidism, and to monitor thyroid medication dosing.
Common errors with this code
What goes wrong on real bills.
Most bills that look correct still contain at least one of these issues. Up to 49% of medical bills contain errors (CFPB).
- Billing 84439 (free T4) alongside 84436 (total T4) when both were not separately ordered and justified — payers may deny one as duplicative
- Confusing 84439 (free T4) with 84480 (T3 total) or 84481 (free T3) — each thyroid hormone fraction has its own CPT code
- Billing free T4 as part of a bundled thyroid panel without verifying that the payer recognizes and pays the panel rather than individual components
If you see 84439 on your bill
Three steps before paying.
1. Get the itemized bill. If your statement only shows a summary, request the CPT-level itemized bill before paying. Generate the request language →
2. Cross-check against the EOB. Compare what your insurer's Explanation of Benefits says you owe versus what the hospital is asking. They disagree more often than people think. Read the bill-vs-EOB guide →
3. Run a free Bill Scan. Upload the bill (and EOB if you have it) and BillBusted will flag the most likely issues with this specific code in your specific state. Run free scan →
Related codes
Other codes in this category.
People who land on 84439 often also see these adjacent codes on the same bill.
CPT
80050 — General health panel; includes CBC w/diff, CMP, TSH
Lab — check for unbundling and duplicate billing.
CPT
80051 — Electrolyte panel; CO2, chloride, potassium, sodium
Lab — check for unbundling and duplicate billing.
CPT
80053 — Comprehensive metabolic panel
If individual blood tests are also on your bill, you may have an unbundling error.
CPT
80055 — Obstetric panel; CBC w/diff, HBsAg, rubella Ab, syphilis, RBC Ab screen, ABO/Rh
Lab — check for unbundling and duplicate billing.
CPT
80061 — Lipid panel (cholesterol)
If you see HDL or LDL listed separately next to 80061, that's unbundling.
Related BillBusted guides
Plain-English reads if you see 84439 on a bill.
84439 FAQ
Plain-English answers.
What does 84439 usually cost?
$10–$22 Medicare allowed (CMS CLFS); $15–$60 commercial; varies by region. Costs vary by region, payer contract, and whether the service was performed in a hospital outpatient department (which adds a facility fee) versus a free-standing clinic.
What's the most common billing error on 84439?
Billing 84439 (free T4) alongside 84436 (total T4) when both were not separately ordered and justified — payers may deny one as duplicative
What should I do if I see 84439 on my bill?
Request the itemized bill and the matching EOB from your insurer. Compare the units/quantity billed against what you actually received. Run a free BillBusted scan to flag the most likely errors specific to 84439 before paying.
Don't pay 84439 blindly.
The free scan tells you in under 60 seconds whether this charge looks reasonable for your situation.