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Add a report from your GP, the NHS App or a clinic, and see your results, medicine and how you feel over time. We explain each level in plain words, read against the lab’s own range. Members watch these films in the app, beside their own results.
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The film in words
A usual thyroid blood test looks at TSH and free T4, and sometimes free T3. Many labs test TSH first, and only add the others if it isn’t normal.
Guidance for doctors is to test TSH first. If TSH is above range, free T4 is tested from the same blood sample. If it’s below range, free T4 and free T3 are.
A TSH above range means the body is asking the thyroid for more hormone.
A high TSH with a low free T4 suggests an underactive thyroid that needs treatment.
A high TSH with free T4 in range is called a mildly underactive thyroid.
Each lab gives a range: what it sees in most healthy people. Your result is compared with it.
Lab ranges are only a guide and vary from lab to lab, so each result is read against the range on its own report.
People may feel well even when their thyroid tests are outside the range.
High-dose biotin supplements can make thyroid test results wrongly high or low.
The British Thyroid Foundation quotes the American Thyroid Association’s advice to stop biotin supplements two days before a thyroid blood test.
Guidance for doctors is not to test the thyroid during a sudden illness, unless the thyroid may be the cause, because the illness can affect the results.
Sources: British Thyroid Foundation: thyroid function tests; NICE NG145; British Thyroid Foundation: diets and supplements
More films
How your thyroid worksThe gland, its two hormones, and the signal from the brain that runs it.1 min 15
Hashimoto’s: why the thyroid slows downThe immune system, TPO antibodies, and why the test isn’t repeated.1 min 04
Levothyroxine, and how to take itWhat it does, taking it so it’s absorbed, missed doses, and why changes take time.1 min 41
Still not feeling right?When results are in range but symptoms aren’t, and what to ask your GP.1 min 16
Basic and full thyroid testsWhat TSH, free T4, free T3 and the two antibodies each add.1 min 33
Lab ranges and your reportThe units on a report, typical ranges as a guide, age, and antibody cut-offs.1 min 17
TPO antibodies, in detailWhat a positive result can mean, with or without a thyroid problem, and why it stays.1 min 11
Tg antibodies, in detailThyroglobulin, why it’s watched after thyroid cancer, and what its antibodies change.58 sec
Iron, B12 and vitamin DOther results you may have, why they come up with the thyroid, and coeliac disease.1 min 25
Pregnancy and your thyroidPlanning a pregnancy, the dose and tests in pregnancy, and after the birth.1 min 33
General information, not a diagnosis. Your GP can tell you what your results mean for you.