Free T4 is thyroxine, the main hormone your thyroid makes, in the unbound form your body can use. Read with TSH, it shows whether your thyroid is making too little, too much or about the right amount, and a low free T4 with a high TSH is the classic pattern of an underactive thyroid. The lab range is 10 to 25 pmol/L, and we aim for 12 to 22 pmol/L. Free T4 comes in the Perimenopause or Menopause Hormone Test ($299 each) or the Weight Management Test ($349), added to your Baseline, and in the Full Body Health Check ($499 with your Baseline). Free T4 itself has no Medicare rebate.
Free T4 adds the thyroid output measure to your TSH. It is included in Vively's Full Body Health Check and our Weight Management, Female Hormone, Perimenopause and Menopause Hormone Tests. You start with your Baseline Health Check.
Every marker in range? Get your $99 back. T&Cs apply.Want to save 25%? Try our 4-Month Reset insteadFree T4 (free thyroxine) is the share of thyroxine in your blood that isn't bound to carrier proteins. Thyroxine is the main hormone your thyroid makes, and most of it is held by proteins, with less than 0.1% circulating free. That free share is what your tissues can take up and turn into the active hormone, free T3.
Your thyroid makes T4 when the pituitary gland in your brain sends thyroid-stimulating hormone (TSH). Each T4 molecule carries four iodine atoms, which is why your thyroid needs iodine.
T4 is best thought of as a reserve. It lasts about a week in the blood, so it changes slowly, which is why doctors wait around six weeks after a dose change before rechecking.
A free T4 test shows how much hormone your thyroid is putting out. Read with TSH, it tells your doctor whether the thyroid is underactive, overactive or working normally.
TSH, the thyroid marker in your Baseline, is very sensitive, because the pituitary turns it up or down in response to small changes in thyroid hormone. Free T4 adds the detail, and the pair together show whether a problem starts in the thyroid or the pituitary.
Thyroid hormone sets the pace of your metabolism, so free T4 is linked to energy, body temperature, heart rate, bowel habit, periods, mood and cholesterol. An underactive thyroid is one of the reasons doctors check thyroid function when LDL cholesterol rises.
Normal does not always mean optimal. A free T4 at the bottom of the range with a TSH drifting upwards is worth tracking, even when both are technically normal.
For adults, free T4 is usually 10 to 25 pmol/L.
| Range | |
|---|---|
| Typical lab reference range (adults) | 10 to 25 pmol/L |
| Vively optimal range | 12 to 22 pmol/L |
Free T4 ranges depend on the lab's method, and some Australian labs use an upper limit closer to 20 pmol/L, so check the range on your report. Optimal ranges are what we aim for to support long-term health, not diagnostic cut-offs.
A high free T4 with a low TSH usually means an overactive thyroid (hyperthyroidism) or an inflamed thyroid leaking stored hormone (thyroiditis). It needs a GP to find the cause. A high free T4 with a normal TSH is more often a testing issue.
Everyday reasons to rule out first:
Medical causes a doctor will look for:
A low free T4 with a high TSH usually means an underactive thyroid (hypothyroidism). In Australia, the most common cause is Hashimoto's thyroiditis, an autoimmune condition. A low free T4 with a low or normal TSH needs a GP to check the pituitary.
Other causes:
Biotin, medication timing, pregnancy and recent illness are the biggest things to plan around.
Do you need to fast? No. If you're testing with the Full Body Health Check, you'll fast anyway for glucose and insulin. Testing at a similar time each round makes your results easier to compare.
Free T4 is always read with TSH first, then with free T3.
| Pattern | What it can mean |
|---|---|
| High TSH, low free T4 | An underactive thyroid (hypothyroidism), most often Hashimoto's. Needs GP review. |
| High TSH, normal free T4 | A milder, early underactive pattern (subclinical hypothyroidism). Usually rechecked in a few months. |
| Low TSH, high free T4 and/or free T3 | An overactive thyroid or thyroiditis. Needs prompt GP review. |
| Low or normal TSH, low free T4 | Can follow a recent illness, or point to the pituitary. Needs GP review. |
| Normal TSH and free T4, but you have symptoms | Your thyroid is unlikely to be the cause. Worth checking ferritin, iron, vitamin B12, glucose and sleep. |
If your free T4 is low because of Hashimoto's or another thyroid condition, food and lifestyle won't fix it, and medication is the right tool. What you eat still matters for making thyroid hormone and for how well treatment works.
See your GP if your free T4 is outside your lab's range, especially with an abnormal TSH, or if you have symptoms of an underactive thyroid (tiredness, feeling cold, weight gain, constipation, heavy periods) or an overactive thyroid (racing heart, weight loss, tremor, feeling hot, anxiety).
Book in promptly for a fast or irregular heartbeat, chest pain, breathlessness, bulging or sore eyes, or a new neck lump. If you're pregnant, have any abnormal free T4 reviewed soon.
Your Baseline Health Check screens TSH. Free T4 is added in our Full Body Health Check, together with free T3, and in our Weight Management Test, Female Hormone Health Test, and Perimenopause and Menopause Hormone Tests. The exact markers can depend on the referring doctor's review.
We arrange your referral through our GP network, and you have one blood draw at one of 3,700+ accredited partner collection centres. Results arrive in the app, usually within a few days. Your practitioner looks at free T4 next to your TSH and our optimal ranges, flags anything your GP should see, builds a personalised plan, and you retest to track change.
Check your free T4 with the Full Body Health Check.
No, free T4 doesn't need fasting. If it's part of a test with fasting markers, such as Vively's Full Body Health Check, you'll fast overnight anyway. Stop biotin supplements for a couple of days beforehand after checking with your doctor, and ask your GP whether to take levothyroxine before or after your blood test.
TSH is the signal from your pituitary gland telling your thyroid to work. Free T4 is the hormone your thyroid makes in response. TSH is the more sensitive screening test, and free T4 shows how much hormone is reaching your blood. Reading both together shows where a problem starts.
It is slightly below the typical range of 10 to 25 pmol/L, though some labs set their lower limit around 9. If your TSH is high, it suggests an underactive thyroid and needs GP review. If your TSH is normal or low, it may reflect recent illness, lab variation or, less often, a pituitary issue.
Yes. High-dose biotin can interfere with some thyroid tests, making free T4 and free T3 look falsely high and TSH falsely low. This can mimic an overactive thyroid. Stop biotin for a couple of days before your test after checking with your doctor, and tell your practitioner you take it.
Many blood tests can be Medicare-funded when a doctor orders them for a clinical reason. With Vively, we arrange the referral through our GP network, so you don't need a separate GP visit first. Your own GP can also order free T4 with TSH for a clinical reason.
No. Vively helps you understand and track your thyroid results, and our practitioners will tell you when something needs medical review. You should still see your GP for diagnosis, thyroid medication, pregnancy care and symptoms that need a doctor. If your results point that way, we'll tell you.
Among 1,692 Vively members tested in 2024 to 2026, women aged 40 to 49 had a median free T4 of 15.3 pmol/L (middle half 14.0 to 17.0). Men the same age: 16.9 pmol/L. The lab range is 10.0 to 25.0 pmol/L. A member median is not a target.
The line is the median member at each age. The shaded bands show where most members sit. The dashed red lines are the lab range.
| Group (pmol/L) | Members | Median | Middle 50% | 5th to 95th percentile | Lab range |
|---|---|---|---|---|---|
| Women 18 to 29 | 72 | 16.0 | 14.5 to 17.7 | 11.3 to 19.3 | 10.0 to 25.0 |
| Women 30 to 39 | 280 | 15.7 | 14.0 to 17.0 | 12.1 to 19.7 | 10.0 to 25.0 |
| Women 40 to 49 | 347 | 15.3 | 14.0 to 17.0 | 11.9 to 19.0 | 10.0 to 25.0 |
| Women 50 to 59 | 259 | 15.9 | 14.0 to 17.0 | 11.6 to 20.0 | 10.0 to 25.0 |
| Women 60 and over | 136 | 15.8 | 14.0 to 17.0 | 12.0 to 19.1 | 10.0 to 25.0 |
| Men 18 to 29 | 70 | 16.9 | 15.1 to 18.0 | 13.0 to 20.5 | 10.0 to 25.0 |
| Men 30 to 39 | 170 | 17.0 | 15.3 to 18.6 | 13.0 to 21.0 | 10.0 to 25.0 |
| Men 40 to 49 | 186 | 16.9 | 15.0 to 18.0 | 13.0 to 21.3 | 10.0 to 25.0 |
| Men 50 to 59 | 113 | 16.7 | 15.1 to 18.0 | 12.8 to 19.9 | 10.0 to 25.0 |
| Men 60 and over | 59 | 16.0 | 15.0 to 18.0 | 13.0 to 23.0 | 10.0 to 25.0 |
Pick your sex and age, then type your result.
What is a normal free T4 level for my age?
Among 1,692 Vively members (first blood test, January 2024 to October 2026), the median free T4 for women was 16.0 pmol/L at 18 to 29, 15.7 at 30 to 39, 15.3 at 40 to 49, 15.9 at 50 to 59 and 15.8 at 60 and over. For men it was 16.9 pmol/L at 18 to 29, 17.0 at 30 to 39, 16.9 at 40 to 49, 16.7 at 50 to 59 and 16.0 at 60 and over.
The lab range is 10.0 to 25.0 pmol/L. A member median is not a target or a diagnosis. If your result is outside the range on your report, talk to your GP.
How to get it: Available as one of our specialty add-on tests. Your test referral is issued straight away when you order. See how a blood test without a referral works.
Add-on test: Thyroid Panel
Related tests: Free Triiodothyronine (T3), FT3 / FT4 Ratio, TSH / T4 Ratio, Thyroid Stimulating Hormone (TSH)
Learn more: What your thyroid results can mean
What your result means: What your pre-pregnancy blood test results can mean
What your result means: What your hormone results can mean
Guide: TSH and free T4 levels by age, including free T4 by age.
The Baseline Health Check reads 70+ markers, then your dietitian turns your results into a plan. $99 a month, first test included.
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