What it calculates

This tool reads your TSH and FT4 against your lab's reference range. It tells you which common pattern the result fits and links to a plain-language article. It is an explainer, not a diagnosis.

What your result means

TSH is the signal from the brain asking the thyroid to work. FT4 is the thyroid hormone itself. Doctors read the two together: for example, a high TSH with a normal FT4 is one pattern, and a high TSH with a low FT4 is another. The tool names the pattern and explains it in plain language. Start with what a high TSH with a normal T4 means or the overview in the thyroid function test explained.

Using your own lab range

Reference ranges differ between labs and in pregnancy. If your report prints a range, enter it in the optional boxes. If your report gives FT4 in pmol/L, divide it by 12.87 to get ng/dL before entering it.

Limits of this tool

A single report is a snapshot. Recent illness, some medicines, biotin supplements taken before the blood draw and the time of day can all move the numbers. Doctors usually repeat a test before drawing a conclusion. The pattern name is a description, not a diagnosis, and this tool cannot say whether you need treatment.

When to talk to a doctor

Share any report outside the normal range with your doctor, and do so promptly if you are pregnant or have symptoms. Do not start, stop or change thyroid medicine based on this tool.

How this tool works

Formula: Pattern lookup: TSH and FT4 are each compared with the lab reference range (low, normal or high). Defaults: TSH 0.4 to 4.5 mIU/L, FT4 0.8 to 1.8 ng/dL.
Source: American Thyroid Association hypothyroidism guideline 2014 (Jonklaas J et al. Thyroid 2014)
Version: 1.0.0

This tool does not replace a consultation. Results are general information; your doctor interprets them with your history and examination.

When to see an endocrinologist

You are pregnant or planning pregnancy
Your FT4 is far outside the lab range, or you have a racing heart, severe tiredness or a fast-growing neck swelling

Chest pain, fainting, severe breathlessness or confusion: call 108 or 112, or go to the nearest emergency department.

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Thyroid report reader