​Blood tests are one of the most important tools used to diagnose and monitor thyroid conditions. However, seeing results such as TSH, T4 or T3 on a blood test report can be confusing, particularly when you are trying to understand what they mean for your thyroid health.

The thyroid gland produces hormones that help regulate many processes throughout the body. When the thyroid produces too little hormone, this is known as hypothyroidism. When it produces too much, it is known as hyperthyroidism. Thyroid function tests help healthcare professionals assess how well the thyroid is working and whether treatment may be needed.

TSH, or thyroid stimulating hormone, is usually one of the main tests used to assess thyroid function. It is produced by the pituitary gland and signals the thyroid to produce thyroid hormones. In general, a higher TSH can indicate that the thyroid is not producing enough hormone, while a lower TSH can be associated with an overactive thyroid. However, thyroid results need to be interpreted in context rather than viewed as a single number.

T4, or thyroxine, is one of the main hormones produced by the thyroid. A blood test can measure free T4, commonly written as FT4, which represents the hormone available for the body's tissues to use. T3, or triiodothyronine, is another thyroid hormone and may be measured in certain circumstances, particularly when hyperthyroidism is suspected or when someone is taking T3 medication.

Thyroid blood tests can also be used to monitor people who are already receiving treatment. The appropriate tests and how frequently they are needed can vary depending on the individual's diagnosis, treatment and circumstances.

If you receive thyroid blood test results that you do not understand, discuss them with your healthcare professional rather than trying to interpret them independently. Reference ranges can also vary between laboratories.

For accessible information about thyroid function testing, diagnosis and treatment, the British Thyroid Foundation provides a range of patient resources and leaflets.
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