This test is for people who are concerned that they may have a thyroid problem.

Early signs and symptoms of thyroid dysfunction may often be very non-specific. The common symptoms hypothyroidism may include:

• Unexplained weight gain
• Dry skin
• Feeling cold
• Puffy skin
• Hair loss
• Tiredness

Some signs and symptoms of hyperthyroidism may include:

• Fast heart rate
• Anxiety
• Unexplained weight loss
• Feeling hot
• Hand tremors
• Bulging, dry, puffy or irritated eyes
• Difficulty sleeping (insomnia)

Our thyroid test will report your levels for all three hormones (TSH, FT4 and FT3). You will receive a personalised interpretation of what the results mean and what you should do about them. This may be as simple as; all is well, to a recommendation to see your GP if we detect an abnormality.

In hypothyroidism, the thyroid gland does not produce sufficient thyroid hormone, so the FT4 and FT3 levels are low.

This causes an increase in TSH to try and stimulate the thyroid to produce more thyroxine.

In hyperthyroidism the thyroid gland produces too much thyroxine, so the T4 levels are high. This causes a decrease in TSH to try and stop the thyroid producing more thyroxine.

Thyroid Peroxidase Antibodies (TPO) can help to see if an underactive thyroid is likely to be caused by autoimmune disease. TPO antibodies are especially useful if someone has a mild form of underactive thyroid called subclinical hypothyroidism. If someone has subclinical hypothyroidism and positive TPO antibodies then they may be more likely to develop an underactive thyroid in the future. More information can be found on our TPO test page.

Being unwell can impact thyroid test results. We would recommend waiting 3 to 4 weeks after recovering from illness or infection before doing our thyroid tests.

Supplements that contain biotin (also known as vitamin B7) can sometimes affect thyroid testing. We recommend leaving the following amount of time between biotin supplement and our blood test:

Less than 10,000 mcg/day (10 mg/day) of biotin – 24 hours

10,000 mcg/day or above (10 mg/day or above) of biotin – 72 hours

There is no need to stop taking thyroid medication before doing this test. It will not change the accuracy of the test.

We provide comments to help you understand your thyroid results and to tell you when we think you should see your doctor. Our comments only apply to people who have not been diagnosed with a thyroid condition and are not on thyroid medication. This is because the monitoring of thyroid disorders needs to look at results together with how you are feeling e.g. ongoing symptoms. For this reason, we are unable to give advice about treatments or the amount you are taking.

Ticking the "taking thyroid medication" box does not change how we process or analyse the sample. It also does not change the normal ranges we provide. It will just stop us from providing a comment with the result that would likely not be relevant to your individual treatment.

TPO antibodies of 35 or above:

You have raised levels of TPO antibodies. If your thyroid tests show a subclinical hypothyroid pattern, this suggests that you may have a higher chance of developing an underactive thyroid in the future. If you have already been diagnosed with an underactive thyroid, this suggests that this condition is caused by an autoimmune disease affecting the thyroid.

TPO antibodies of 34 or below:

You have normal levels of TPO antibodies. If your thyroid tests show a subclinical hypothyroid pattern, this suggests that you have a lower chance of developing an underactive thyroid in the future.

If you have already been diagnosed with an underactive thyroid, this result does not indicate whether or not this condition is caused by an autoimmune disease affecting the thyroid. Up to 1 in 10 people with an autoimmune underactive thyroid condition have TPO antibodies within the normal range (i.e. 34 or below).

It is not clear what a high level of TPO antibodies means for someone with normal thyroid tests. There is some evidence to indicate that high levels of TPO antibodies could suggest a higher chance of developing an underactive thyroid in the future. However, many people with high levels of TPO antibodies will not go on to develop an underactive thyroid.

We do not report a numeric value below the cut-off of 35 imU/mL. The reason for this is that a large number of healthy individuals have detectable TPO in this range and it is just background ‘noise’. These low levels of TPO are not associated with thyroid disorders, can lead to confusion and in some cases the assumption that values in this range may be significant.

For all positive results we do report a numeric value.

TPO antibodies are present in the majority of people with hyperthyroidism but this is not helpful for determining the cause of hyperthyroidism. If your test results indicate that you have hyperthyroidism then we recommend discussing the result with your doctor. 

Thyroglobulin antibodies also known as anti-thyroglobulin antibodies are another test related to the thyroid. Studies have demonstrated that TPO antibodies are linked to an underactive thyroid. The same studies found that thyroglobulin antibodies were only associated with an underactive thyroid in people who also had positive TPO antibodies. When thyroglobulin antibodies were found on their own they were not associated with an underactive thyroid. For this reason, we do not feel that measuring thyroglobulin antibodies adds any information above measuring TPO antibodies alone and so is not of benefit to our customers.

The ranges are represented visually on the chart, when viewed on a desktop pc, so you can see exactly where your result lies in relation to the ranges.

The ranges are:

TSH 0.27 to 4.20 mIU/L

FT4 12.0 to 22.0 pmol/L

FT3 3.1 to 6.8 pmol/L

TPO 35 IU/mL and above is positive

Thyroid Stimulating Hormone (TSH) - Roche Cobas Elecsys TSH electrochemiluminescence immunoassay

Thyroxine (T4, free direct) - Roche Cobas Elecsys FT4 III electrochemiluminescence immunoassay

Triiodothyronine (T3, free) - Roche Cobas Elecsys FT3 III electrochemiluminescence immunoassay

Thyroid peroxidase antibodies – Roche Cobas Elecsys Anti-TPO electrochemiluminescence immunoassay

All four tests are analysed on a Roche Cobas e801 analyser