T3 Uptake Test Cost and Medicare Coverage (CPT 84479)

Also called: T3 resin uptake · T3RU · resin T3 uptake · thyroid hormone-binding ratio · T uptake — all the same test, CPT 84479.

The short answer

Yes, under the same national thyroid policy as the TSH and free T4, with the same twice-a-year rhythm for stable patients. Medicare’s thyroid policy (NCD 190.22, the same in every state) names this test outright. It describes the standard workup as TSH “complemented by determination of thyroid hormone levels [free thyroxine (fT-4) or total thyroxine (T4) with Triiodothyronine (T3) uptake],” and adds: “When a test for total thyroxine (total T4 or T4 radioimmunoassay) or T3 uptake is performed, calculation of the free thyroxine index (FTI) is useful to correct for abnormal results for either total T4 or T3 uptake due to protein binding effects.”

That sentence is also the reason this is a test you may never be offered. T3 uptake is not a measure of T3 at all. It estimates how much room is left on the proteins that carry thyroid hormone, and it exists to be combined with a total T4 into the free thyroxine index, an older way of estimating free T4. MedlinePlus says so directly: “Because tests called the free T4 blood test and thyroxine binding globulin (TBG) blood tests are now available, the T3RU test is rarely used these days.” Quest’s own clinical guide lists it with the note “(rarely used).” The rule to know is the frequency: “Testing may be covered up to two times a year in clinically stable patients.”

When Medicare DOES cover it

The national policy’s covered picture, in plain English:

• Diagnosing thyroid disease. The policy says thyroid testing may be reasonable and necessary to “confirm or rule out primary hypothyroidism,” “confirm or rule out primary hyperthyroidism,” and “distinguish between primary and secondary hypothyroidism.”
• Monitoring treatment. To “monitor drug therapy in patients with primary hypothyroidism,” “monitor therapy in patients with hyperthyroidism,” and “monitor thyroid hormone levels (for example, patients with goiter, thyroid nodules, or thyroid cancer).”
• Working up symptoms. The policy’s list is long: “metabolic disorders; malnutrition; hyperlipidemia; certain types of anemia; psychosis and non-psychotic personality disorders; unexplained depression; ophthalmologic disorders; various cardiac arrhythmias; disorders of menstruation; skin conditions; myalgias,” and “a wide array of signs and symptoms.”
• Long-term follow-up. “Follow-up thyroid testing in patients with a personal history of malignant neoplasm of the endocrine system and in patients on long-term thyroid drug therapy.”
• As the partner of a total T4. The policy’s own description pairs T3 uptake with total T4 so the free thyroxine index can be calculated. Quest’s directory says the assay “should be interpreted with thyroxine levels,” and Labcorp’s says “it should never be used alone; rather, its usual application is use with thyroxine (T4).”

If one of these genuinely describes your situation, the diagnosis for it belongs on your doctor’s order, and coverage follows.

When Medicare does NOT cover it

• More than twice a year for a stable patient. “Testing may be covered up to two times a year in clinically stable patients; more frequent testing may be reasonable and necessary for patients whose thyroid therapy has been altered or in whom symptoms or signs of hyperthyroidism or hypothyroidism are noted.”
• Pure routine screening with nothing thyroid-related in the picture. The policy ties every covered use to a diagnosis, a treatment, or a symptom, and Quest’s clinical guide adds that “screening is not recommended in the general population.”

(Never ask anyone to change a code just to get coverage; that is fraud. But doctors often have a legitimate reason for the test that simply wasn’t written down.)

What you pay if it IS covered: $0

Covered lab tests cost Medicare patients nothing, with no deductible and no 20% coinsurance. Medicare pays the lab $6.47 for a T3 uptake test, and you owe zero.

What you pay if it is NOT covered, read this before you sign

Quest’s own test directory flags T3 uptake as “subject to a Medicare Limited Coverage Policy” that “may require a signed ABN when ordering.” (Labcorp’s page carries no such notice.) If T3 uptake is on your order as a third thyroid check in a year with no change in your dose or symptoms, or with nothing thyroid-related on the order at all, expect the Advance Beneficiary Notice (ABN), the signature pad, committing you to the lab’s own billing rates if Medicare denies the claim. Before you sign:

1. Ask the lab to print exactly what you would owe. You’re entitled to see the number in black and white first. For perspective: when Medicare covers this exact test, it pays the lab $6.47.
2. Ask why this test and not a free T4. Both the national policy and the lab directories describe T3 uptake as a companion to total T4; if the order carries a free T4 already, ask what the uptake adds.
3. Know the direct prices: T3 uptake sells for $5 at Jason Health (jasonhealth.com, plus their flat $18 lab-collection fee per order, so $23 all in) and $15.95 at Ulta Lab Tests (partner link in the table; our commission is disclosed there; add their $12.95 draw fee). Quest’s consumer site and Labcorp OnDemand do not sell it, and Personalabs sells it only inside a thyroid panel. Same certified labs, same blood draw.

Before you sign the pad, 60-second checklist

1. Ask: “Can you print what I’ll owe if Medicare doesn’t pay?”
2. Ask your doctor: “Is this my first or second thyroid check this year, or has my dose or my symptoms changed, and is that on the order?”
3. Compare the printed price to the direct-purchase prices before deciding how to proceed.

What counts as a “normal” T3 uptake result

Start with the range printed on your own report. There is no published standard to compare it with, and for this test the lab-to-lab differences are unusually visible, because the result is a percentage that depends on each lab’s method:

• MedlinePlus: “Normal values range from 25% to 38%.”
• Labcorp’s reference interval is 24 to 39% for ages 18 and over.
• Quest’s reference range is 22 to 35%.

No medical body publishes a target for T3 uptake, and the result is not read alone in any case. Labcorp calls it “an indirect measure of binding protein” that “reflects available binding sites,” and Quest says the assay “is a measure of available thyroid hormone binding sites and should be interpreted with thyroxine levels.” The number moves with the carrier proteins, not only with the thyroid. MedlinePlus lists pregnancy and estrogen among the things that lower it and kidney failure, protein malnutrition, and chronic liver disease among the things that raise it, and Labcorp lists “major illness, high-dose salicylates, corticosteroids,” several other drugs, “pregnancy, oral contraceptives, and hormonal therapies” as reasons the binding capacity changes.

(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 TSH, your T4, and your history.

Quick questions people ask

What does a T3 uptake test measure? Not T3. MedlinePlus: “The T3RU test measures the level of proteins that carry thyroid hormone in the blood.” Labcorp: “T3 uptake is not a measurement of serum T3.” The American Thyroid Association explains why that matters: “T4 and T3 circulate almost entirely bound to specific transport proteins. If the levels of these transport proteins changes, there can be changes in how much bound T4 and T3 is measured.” T3 uptake is the lab’s estimate of how full those transport proteins are. On billing paperwork it is CPT code 84479; Quest’s directory lists it as “Resin Uptake,” “T3 Resin Uptake,” “T3RU,” and “T3 Index,” and Labcorp bills it under the name “Thyroid Hormone Binding Ratio” at some locations.

Why is it called an older test? Because of what replaced it. The uptake exists to be multiplied against a total T4 to produce the free thyroxine index (FTI, sometimes T7), an estimate of the hormone that is actually free. The American Thyroid Association says tests measuring free T4, “either a free T4 (FT4) or free T4 index (FTI),” reflect thyroid function more accurately than a total T4, and Cleveland Clinic says “healthcare providers most often use a free T4 test to assess thyroid function because it’s more accurate than a total T4 test.” Once labs could measure free T4 directly, the two-step estimate lost its job. MedlinePlus: the T3RU test “is rarely used these days.” Quest’s clinical guide marks it “(rarely used)” but still sells it, alone and inside a thyroid panel that “includes T3 uptake, total T4 (thyroxine), and free T4 index (T7).”

How is T3 uptake different from a T3 test? A T3 test measures the hormone triiodothyronine itself. Cleveland Clinic describes two forms, “free T3,” which “enters your body’s tissues where it’s needed,” and “bound T3,” which “attaches to proteins.” T3 uptake measures neither; it measures the room on the proteins. The shared name is the confusing part, and it is why Quest’s directory keeps “T3 (Triiodothyronine)” among the aliases for this test.

Do you have to fast for a T3 uptake test? No. Quest’s directory lists patient preparation as “none specified,” and Ulta’s page says “no preparation required.” MedlinePlus asks you to tell your provider about the medicines you take, because “anabolic steroids, heparin, phenytoin, warfarin” can raise the result and “antithyroid medicines, birth control pills, estrogen” can lower it, and not to stop any medicine on your own. Labcorp adds that high-dose biotin supplements can interfere and asks patients to stop biotin “at least 72 hours prior to sample collection.” Our fasting guide covers what fasting means when a different test on the same order needs it.

Sources and data dates

Medicare payment amount: CMS Clinical Laboratory Fee Schedule, 2026 Q3 file (national rate for 84479). Coverage rules: CMS Medicare Coverage Database, NCD 190.22 (Thyroid Testing), a national policy identical in every state, and the same text in the NCD Manual, Chapter 1, Part 3. Test descriptions, preparation, and ranges: MedlinePlus Medical Encyclopedia (T3RU test), American Thyroid Association (Thyroid Function Tests), Cleveland Clinic (T4 Test; T3 Test), Quest test 861 and the Quest Clinical Focus on thyroid dysfunction, Labcorp test 001156. Consumer prices 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.