What the value means
TSH is a pituitary hormone that drives the thyroid – when the gland works more slowly, TSH rises. The reference range is roughly 0.4–4.0 to 4.5 mIU/L, but laboratories differ. Your value is in the upper part of the range. Some experts have proposed lowering the upper limit to 2.5 mIU/L, but major professional societies have not adopted this for the general population, because there is no evidence that treatment in this band brings benefit. TSH naturally rises slightly with age and fluctuates during the day – it tends to be higher in the morning and after poor sleep. Pregnancy and planning a pregnancy are an exception, with stricter targets.
Possible causes
- Normal variability – time of sampling, sleep, a recent illness or stress can shift the value.
- Early autoimmune thyroiditis – Hashimoto’s often first appears as a slightly higher TSH with positive anti-TPO antibodies.
- Iodine – both deficiency and excess can affect thyroid function.
- Age – a slightly higher TSH is common and often harmless in older people.
- Medicines and supplements – some medicines change TSH; biotin can distort laboratory results.
What you can do
- Add tests – fT4, anti-TPO and possibly fT3; TSH alone is not enough.
- Repeat the test – in 6–8 weeks, in the morning, fasting and at the same laboratory.
- Pause biotin – if you take biotin-containing supplements, ask how long to pause them before the blood draw.
- Diet – iodised salt in sensible amounts, fish, eggs; selenium from a varied diet. Do not take high-dose iodine supplements without reason.
- Sleep and stress – a regular routine helps results reflect your true state.
When to see a doctor
See a doctor if you have fatigue, feel cold, gain weight, have constipation, dry skin, hair loss, cycle problems or an enlarged thyroid, if anti-TPO is positive, if thyroid disease runs in your family, or if you are planning a pregnancy or are pregnant. A TSH repeatedly above the upper limit should always be discussed with a doctor.