Typical reference ranges
| Test | Typical adult range | Other units |
|---|---|---|
| TSH | 0.4–4.0 mIU/L | Same number in µIU/mL |
| Free T4 (FT4) | 0.8–1.8 ng/dL | 10–23 pmol/L |
| Free T3 (FT3) | 2.3–4.2 pg/mL | 3.5–6.5 pmol/L |
| Total T4 | 5.0–12.0 µg/dL | 64–154 nmol/L |
| Total T3 | 80–200 ng/dL | 1.2–3.1 nmol/L |
Ranges based on: MedlinePlus; American Thyroid Association; NICE NG145. Full references are listed at the end of this page.
Use your own lab's range. Reference ranges differ between labs, analysers and methods, and with age, sex and pregnancy. The range printed on your report takes priority over the figures here.
Check your value
Type the Free T4 result from your report to see where it sits against the typical ranges on this page. Nothing is sent or saved.
General information only, not a diagnosis. Your lab's printed range takes priority.
Tests in this panel
Which tests are in a thyroid profile?
TSH is the best single screening test. Free T4 is added to confirm and grade a thyroid problem. Free T3 helps mainly when an overactive thyroid is suspected. Many labs in Pakistan and India still offer total T3 and T4, which are affected by binding proteins (for example in pregnancy or with the contraceptive pill), so free hormone tests are usually preferred.
Common result patterns
- High TSH, low free T4: underactive thyroid (hypothyroidism), most often from Hashimoto's thyroiditis.
- High TSH, normal free T4: subclinical hypothyroidism, often rechecked in 6–12 weeks.
- Low TSH, high free T4 or T3: overactive thyroid (hyperthyroidism), for example Graves' disease.
- Low TSH, normal free T4 and T3: subclinical hyperthyroidism, or too high a thyroxine dose.
Thyroid antibodies (anti-TPO) are sometimes added to look for autoimmune thyroid disease.
Thyroid tests in pregnancy
TSH normally falls in the first trimester. Guidelines advise trimester-specific ranges from the lab; where none exist, an upper TSH limit of about 4.0 mIU/L is commonly used. Women already on thyroxine usually need a dose check as soon as pregnancy is confirmed.
Ranges really do differ between labs
As an example, one NHS laboratory (North Bristol) uses TSH 0.38–5.33 mU/L, free T4 8.0–18.0 pmol/L and free T3 3.7–6.6 pmol/L, a little different from the typical figures above. That is why the range on your own report comes first.
Preparing for the test
No fasting is needed. Stop biotin supplements a few days before if your doctor agrees, as biotin can distort some results. If you take thyroxine, your doctor may ask you to have blood taken before your morning dose.
Frequently asked questions
Do I need to fast for a thyroid test?
No. Morning tests are common but fasting is not required.
What is the difference between T4 and free T4?
Total T4 includes hormone bound to proteins; free T4 is the active, unbound part and is more reliable.
How often should thyroid tests be repeated?
After a dose change, usually after 6–8 weeks. Once stable, often once a year.
Is TSH 5 high?
Slightly above most ranges. It is often rechecked before any decision, especially if free T4 is normal.
Sources and references
- MedlinePlus: Thyroid tests
- American Thyroid Association: Thyroid Function Tests
- NICE NG145: Thyroid disease
- North Bristol NHS Trust: Thyroid function tests (lab reference ranges)