Free Thyroxine (FT4) LIS Code: FT4
Private free T4 (FT4) thyroid blood test £31, results in about 4 hours. Best read with TSH. No fasting or GP referral. Slough, Victoria, Neasden.
Before your test
Good to know: If you take biotin (vitamin B7) or a hair, skin and nails supplement, stop it for 2 days before your test, as it can affect thyroid results.
Test Categories
About this test
Free T4 (free thyroxine) is the main hormone your thyroid makes. "Free" means the part that isn't bound to proteins in the blood, so it's available for your body to use. It controls how fast your body uses energy, which affects your weight, temperature, heart rate, energy and mood.
Why FT4 is read with TSH
Your pituitary gland makes TSH to tell the thyroid how much T4 to make. Looking at the two together shows where a problem is:
- High TSH and low FT4: an underactive thyroid (hypothyroidism). Common signs are tiredness, weight gain, feeling cold, dry skin and low mood.
- Low TSH and high FT4: an overactive thyroid (hyperthyroidism). Common signs are weight loss, a fast heartbeat, anxiety, shaking and feeling hot.
- High TSH with normal FT4: a mildly underactive thyroid, often rechecked after a few months.
- Unusual combinations, such as low TSH with low FT4, can point to the pituitary gland and need a doctor's review.
To look for the cause, such as Hashimoto's or Graves' disease, add TPO antibodies. Our TSH & Free T4 profile tests both from one blood draw, and free T3 is useful when an overactive thyroid is suspected.
Preparing for your test
- No fasting is needed.
- If you take biotin (vitamin B7) or a hair, skin and nails supplement, stop it for 2 days before, as it can affect thyroid results.
- If you take thyroid medicine, follow your doctor's advice on whether to take your dose before the test, and test at a similar time each time.
How it works at VitaLync
- £31 for the test, plus a £25 blood draw at our Slough, Victoria or Neasden clinic, or a nurse visit at home or work.
- The laboratory usually reports FT4 within about 4 hours of receiving your sample, and your result appears in your secure online account.
- To talk your result through, book a GP consultation.
