The thyroid sets the pace of your metabolism, so when it runs slow or fast the effects appear almost everywhere — energy, weight, mood, temperature, heart rate, skin, hair and menstrual cycle.
The difficulty is that those symptoms are shared with anaemia, vitamin D deficiency, sleep problems, depression, and simply being overworked. A blood test is what separates them.
What TSH actually measures
TSH is not a thyroid hormone. It is the signal from the pituitary gland telling the thyroid to work harder, which is why it moves in the opposite direction to what most people expect.
A high TSH usually means an underactive thyroid — the pituitary is shouting because the thyroid is not responding. A low TSH usually means an overactive one. If TSH is abnormal, free T4 and sometimes T3 and thyroid antibodies are checked to complete the picture.
Symptoms worth testing for
No single symptom points reliably at the thyroid. A cluster of them, particularly one that has developed over months, is a reasonable reason to test.
- Underactive: fatigue, weight gain, feeling cold, constipation, dry skin, hair thinning, low mood, heavy periods
- Overactive: weight loss, palpitations, heat intolerance, tremor, anxiety, loose stools, disturbed sleep
Why it matters in pregnancy
Thyroid function has a direct bearing on fertility, miscarriage risk and fetal development, and the reference ranges used in pregnancy differ from the standard ones. Anyone pregnant, planning pregnancy or being investigated for fertility should have thyroid function checked and interpreted against the right range.
What happens if it is abnormal
An underactive thyroid is treated with daily thyroid hormone replacement, adjusted by repeat testing until stable, then reviewed periodically. An overactive thyroid has several treatment routes and usually involves a specialist. Neither is an emergency in most cases, and both are manageable.
Common questions
Can a thyroid problem cause weight gain?
An underactive thyroid can cause moderate weight gain, often with fatigue, feeling cold and dry skin. It is rarely the sole explanation for substantial weight gain, which is why doctors test for it rather than assume it either way.
Is TSH enough on its own?
As a first test, usually yes. If TSH is abnormal, free T4 and sometimes T3 and thyroid antibodies are added to work out what is happening and whether it needs treating.
Do I need to fast for a thyroid test?
No. Timing has a small effect on TSH, so if you are being monitored it is sensible to have repeat tests at a similar time of day.
This article is general health information, not medical advice, and does not replace a consultation. Care at Smart Care Polyclinic is provided by DHA-licensed clinicians.