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TSH Result Interpreter

Understand what your thyroid stimulating hormone (TSH) blood test result means, in plain English — with optional Free T4 cross-check.

📋 Sources: Non-pregnant adult range 0.4–4.0 mIU/L: Med J Aust 2008;189(5). Subclinical hypothyroidism cut-offs (4–10 and above 10): RACGP, Management of subclinical hypothyroidism (revised 1 Nov 2022). Very low TSH (below 0.1): NPS thyroid function testing algorithm (ESA-endorsed). Subclinical vs overt definitions: RACGP and Hormones Australia. Pregnancy: Med J Aust 2008;189(5); RANZCOG C-Obs 46.
Laboratories print their own ranges; use the range on your report. General information only, not a diagnosis and not medical advice. Discuss your result with your doctor.
For patients & clinicians: This is an interpretation aid, not a diagnosis. Thyroid function is assessed alongside symptoms, antibody tests, repeat results over time, and — if pregnant — pregnancy-specific targets that this tool does not use.
TSH (Thyroid Stimulating Hormone)
Enter the value from your pathology report, in mIU/L (milli-international units per litre — the standard Australian unit).
mIU/L
Lab's printed TSH range (optional). Defaults to 0.4–4.0, the adult range cited in MJA 2008;189(5). Labs print their own ranges.
to
Free T4 (optional)
If your report also includes Free T4 (fT4), enter it and the lab's printed normal range for a more specific interpretation. Leave blank to skip.
pmol/L — lab range: to
Currently pregnant?
Pregnancy changes normal TSH ranges by trimester. If yes, this tool will flag that a different range applies rather than attempt to interpret your result.
Currently taking thyroid medication?
E.g. thyroxine (levothyroxine) or a thyroid-suppressing medication such as carbimazole. Changes how your result should be read.

TSH (thyroid stimulating hormone) is made by the pituitary gland in the brain. It tells the thyroid gland, in your neck, how much thyroid hormone (T4 and T3) to produce. TSH is the most sensitive first-line test of thyroid function and is usually checked before other thyroid tests.

TSH and thyroid hormone work on a feedback loop: when thyroid hormone levels are low, the pituitary raises TSH to try to stimulate the thyroid. When thyroid hormone levels are high, the pituitary lowers TSH. This is why a high TSH usually points to an underactive thyroid, and a low TSH usually points to an overactive one.

TSH (mIU/L) General category
<0.1Very low (NPS thyroid testing algorithm)
0.1 to below the low end of the rangeLow
0.4–4.0 (or your lab's range)Within range (MJA 2008)
Above the range, up to 10Above range; RACGP subclinical hypothyroidism band 4–10
>10Above 10 (RACGP)

Sources: MJA 2008;189(5) (0.4–4.0); RACGP, Management of subclinical hypothyroidism (revised 1 Nov 2022); NPS thyroid function testing algorithm (ESA-endorsed). Labs print their own ranges; enter yours above.

When TSH is abnormal but Free T4 is still within its normal range, this is usually called a subclinical pattern — a milder finding. Definitions follow RACGP and Hormones Australia.

  • High TSH + normal Free T4 → subclinical hypothyroidism
  • High TSH + low Free T4 → overt (clinical) hypothyroidism
  • Low TSH + normal Free T4 → subclinical hyperthyroidism
  • Low TSH + high Free T4 → overt (clinical) hyperthyroidism

An unusual combination, such as high TSH with high Free T4 or low TSH with low Free T4, does not fit these patterns. Your doctor interprets such results.

On repeat testing, Hormones Australia describes 6 to 8 weeks and the RACGP describes 2 to 3 months for confirming a subclinical result. Information only.

This tool is not suitable for:

  • Pregnancy — TSH targets change by trimester and should be interpreted by your GP, obstetrician, or endocrinologist using pregnancy-specific ranges (RANZCOG C-Obs 46; MJA 2008;189(5))
  • Children — paediatric reference ranges differ from adult ranges
  • Recent major illness, hospital admission, or recent medication changes — these can temporarily affect thyroid test results independent of true thyroid disease (so-called "sick euthyroid" / non-thyroidal illness patterns)
  • A single result on its own — thyroid function is usually interpreted alongside symptoms, thyroid antibody tests (e.g. TPO antibodies), and a repeat result over time, not one value in isolation

If you are taking thyroid medication, your doctor may use a different target from the range shown here.

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