Thyroid Function Test (TSH, T3, T4)🧪 Thyroid Function Test (TSH, T3, T4)
Evaluates thyroid hormone levels to diagnose or monitor thyroid disorders — a key cause of fatigue, weight changes, and mood issues.
🔍 What is it?
A Thyroid Function Test is a blood test that measures how well your thyroid gland is working. The thyroid is a small gland in your neck that controls your metabolism, energy levels, and body temperature.
These tests can help detect underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid function — both of which can cause a range of symptoms.
📊 What does it measure?
| Marker | What It Does |
| TSH (Thyroid Stimulating Hormone) | Controls how much thyroid hormone is produced; high TSH often means low thyroid function |
| Free T4 (Thyroxine) | Main thyroid hormone; low in hypothyroidism |
| Free T3 (Triiodothyronine) | Active form of thyroid hormone; often measured if hyperthyroidism is suspected |
Some tests also include thyroid antibodies (like TPOAb) to assess for autoimmune thyroid conditions like Hashimoto’s or Graves’ disease.
❓ Why might I need it?
You may be advised to test your thyroid function if you:
- Feel tired, sluggish, or cold all the time
- Notice unexplained weight gain or loss
- Have dry skin, hair thinning, or brittle nails
- Experience low mood or depression
- Have a fast or irregular heartbeat
- Feel anxious or restless
- Are having difficulty conceiving or have irregular periods
- Have a family history of thyroid disease
🧬 Conditions it can help detect or monitor:
- Hypothyroidism (underactive thyroid)
- Hyperthyroidism (overactive thyroid)
- Hashimoto’s thyroiditis (autoimmune hypothyroidism)
- Graves’ disease (autoimmune hyperthyroidism)
- Thyroid nodules or goitre
- Thyroid hormone imbalance during pregnancy
📈 Normal Ranges (NHS guidance):
| Marker | Typical Reference Range |
| TSH | 0.4 – 4.0 mIU/L |
| Free T4 | 9 – 25 pmol/L |
| Free T3 | 3.5 – 7.8 pmol/L |
Ranges vary slightly between labs. TSH is often the first indicator of dysfunction.
⏱️ How is it done?
- A blood sample is taken from a vein in your arm
- The process takes just a few minutes
- Results are usually ready within 1–2 working days
💷 Typical private cost in the UK:
- Basic TSH + Free T4: £40–£70
- Full panel (TSH, T3, T4 + antibodies): £80–£120
Often included in fatigue, weight management, or female hormone health panels.
✅ Commonly combined with:
- Full Blood Count (FBC) – To rule out anaemia
- Vitamin B12 and Iron – For tiredness
- Cortisol (AM test) – For adrenal fatigue
- Sex hormones (oestrogen/testosterone) – For hormonal imbalance
- Liver and kidney function – For overall health monitoring
📚 References:
- NHS UK – Underactive thyroid (hypothyroidism)
- NHS UK – Overactive thyroid (hyperthyroidism)
- British Thyroid Foundation – Thyroid function tests
- NICE CKS – Hypothyroidism