How to read thyroid test results
Quick answer: To read thyroid test results, start with TSH, check free T4 and look at antibodies if tested.
- Start with TSH. About 0.4–4.5 mIU/L is the usual adult range. TSH works backwards: high TSH means the thyroid is slow, low TSH means it's overactive.
- Check free T4. About 0.8–1.8 ng/dL (10–23 pmol/L). A high TSH with low free T4 suggests an underactive thyroid.
- Look at antibodies if tested. Raised anti-TPO points to autoimmune thyroid disease, such as Hashimoto's.
Common patterns
High TSH with normal free T4 is called subclinical hypothyroidism and is often rechecked in a few weeks before treatment. High TSH with low free T4 suggests hypothyroidism. Low TSH with high free T4 or T3 suggests hyperthyroidism. If you take thyroid tablets, TSH shows whether the dose is right.
When ranges are different
Pregnancy, older age, recent illness and some medicines and supplements (including biotin) can change thyroid results. Tell your doctor about these.
Important
This tool explains results in plain words; it can't diagnose anything. Your doctor reads them alongside your symptoms, history and medicines.
Frequently asked questions
Is a TSH of 5 high?
Slightly above the usual range. Mild rises often settle and are usually rechecked, especially if free T4 is normal and you feel well.
What does low TSH mean?
Usually that the thyroid is making too much hormone, or that a thyroid tablet dose is too high.
Why is my lab's normal range different?
Each lab sets ranges for its own machines and methods, so they vary a little. When your report prints a range, the checker shows it and uses it for most tests. For tests with standard medical cut-offs, such as HbA1c, cholesterol and vitamin D, it uses those cut-offs.
Are my results uploaded or stored?
No. The report is read inside your browser, on your device. Nothing is sent to a server or saved after you close the page.