Tired, foggy, flat? Why we check your thyroid.
Thyroid problems produce almost exactly the symptoms women expect from their hormones: fatigue, brain fog, low mood, weight change, feeling cold, and cycles that go haywire. They are far more common in women than men. That is why TSH sits inside our hormone, fertility and fatigue panels rather than off to one side.
There is a small gland at the front of your neck that sets the speed of almost everything in your body. When it runs slow, you feel slow. When it runs fast, you feel wired. Either way, the symptoms are so close to hormonal ones that the thyroid has a fair claim to being the great impersonator of women's health.
How common is it in women?
Thyroid disorders are several times more common in women than in men, and the risk rises with age and in the year after having a baby. A meaningful share of women who believe they have "hormone problems" or early perimenopause turn out to have an under-active thyroid, or both at once.
The common causes in women are autoimmune. In an under-active thyroid the immune system gradually reduces the gland's output, which is why thyroid antibodies are worth checking when TSH is borderline. Thyroid function also shifts during pregnancy and in the months afterwards, which is a frequent reason new mothers feel unwell long past the point they expected to bounce back.
What TSH actually measures
Thyroid-stimulating hormone comes from the pituitary gland in the brain. It tells the thyroid how much thyroid hormone to make. If the thyroid is sluggish, the brain shouts louder and TSH goes up. If the thyroid is over-active, the brain goes quiet and TSH drops. So TSH is a sensitive first-line read on thyroid function, and it moves in the opposite direction to the gland: high TSH suggests under-active, low TSH suggests over-active.
| Marker | Typical Australian adult range | What it usually means |
|---|---|---|
| TSH | About 0.4 to 4.0 mIU/L | The first-line screen. High suggests under-active, low suggests over-active. |
| Free T4 | Laboratory specific | The main circulating thyroid hormone. Added when TSH is abnormal, to show how far. |
| Free T3 | Laboratory specific | The active hormone. Useful mainly when an over-active thyroid is suspected. |
| Thyroid antibodies | Negative or low titre | Point to an autoimmune cause and to the chance of change over time. |
Ranges vary by laboratory; your report shows the range your lab uses. Typical ranges on this page are drawn from Pathology Tests Explained (RCPA) and the sources listed below.
Our companion article on thyroid blood tests explained goes through each marker, the ranges, and the "my TSH is normal but I feel awful" question in detail.
The overlap with hormonal symptoms
- Cycles: an under-active thyroid can make periods heavier, irregular or absent, and can interfere with ovulation and with fertility.
- Energy and mood: fatigue, low mood and brain fog look identical whether the cause is thyroid or perimenopause.
- Weight and temperature: weight gain and feeling cold point towards an under-active thyroid; hot flushes point the other way, and the two can coexist.
- Palpitations and anxiety: classic for an over-active thyroid, and also classic for perimenopause.
- Hair and skin: hair shedding, dry skin and brittle nails appear on both lists, and on the low iron list too.
- Pregnancy: thyroid function matters before and during pregnancy, which is why it is checked in preconception and postpartum panels.
What a result can mean
- In range: reassuring. Your symptoms are unlikely to be thyroid-driven, and the next places to look are usually iron, vitamin D and the cycle hormones.
- Mildly raised: common, and it often settles on a repeat. Your doctor will usually repeat it in six to twelve weeks (often around two to three months), frequently adding free T4 and thyroid antibodies, before deciding anything.
- Clearly raised or low: needs proper assessment. A doctor arranges further testing, discusses what it means, and involves your GP or a specialist as appropriate.
An abnormal TSH is a starting point, not a verdict. What matters is the pattern across TSH, free T4 and antibodies, and how you feel.
Things that affect the reading
Recent illness, pregnancy, the time of day and some supplements can all nudge TSH. High-dose biotin is the notorious one, because it interferes with the assay itself and can push results in either direction; if you take it, tell your doctor, because it may be worth pausing beforehand. TSH is also slightly higher early in the morning, so collecting at a consistent time makes repeat readings easier to compare.
If your KnowLuna result flags your thyroid, your doctor explains exactly what it means and what happens next. You are never left with a red number and no plan.
Common questions
What are early signs of thyroid problems in women?
For an under-active thyroid: fatigue that sleep does not fix, feeling cold, weight gain, constipation, dry skin, hair shedding, low mood and brain fog. For an over-active one: palpitations, anxiety, heat intolerance, weight loss, tremor and poor sleep. Both can change your periods. None of these are specific, which is why a blood test settles the question.
Can thyroid problems affect periods?
Yes, in both directions. An under-active thyroid commonly makes periods heavier, longer or irregular, and can stop ovulation altogether. An over-active thyroid tends to make them lighter or less frequent. An under-active thyroid also raises prolactin in some women, which disturbs cycles further. This is why TSH is checked whenever periods change unexpectedly.
Is TSH enough on its own?
As a first-line screen, usually yes: TSH is the most sensitive single marker, and a clearly normal result makes a thyroid cause unlikely. It is not enough when TSH is borderline, when symptoms are strong, in pregnancy, or when an over-active thyroid is suspected. Then free T4, free T3 and antibodies add the detail.
What should I do if my TSH is high?
Do not act on a single reading. Mildly raised TSH is common and frequently settles, so a doctor typically repeats it after six to twelve weeks with free T4 and antibodies added. A clearly raised result needs proper assessment. Your KnowLuna doctor explains what your number means and what the appropriate next step is.
Is a thyroid test covered by Medicare?
When a GP or specialist requests TSH for a clinical reason, Medicare usually rebates it, and free T4, free T3 and antibodies are rebated only in defined circumstances, such as an abnormal TSH. Consumer-initiated testing, including KnowLuna's, is self-pay and not rebated. If cost is the deciding factor, ask your GP first.
Sources and further reading
- Pathology Tests Explained (RCPA): thyroid function tests
- Pathology Tests Explained (RCPA): thyroid stimulating hormone (TSH)
- Healthdirect: thyroid function tests
- Healthdirect: thyroid problems
- Better Health Channel: thyroid gland
General information only, not medical advice. If your symptoms are severe or sudden, see a doctor promptly. This page does not replace a consultation with a doctor who knows your history; read our medical disclaimer.