Thyroid Function with Antibodies Blood Test

Five markers rather than three. TSH and free T4 show whether the thyroid is under- or over-active. Free T3 is the active form of thyroid hormone and shows how much is actually available to the body, which matters when TSH is low or when symptoms persist despite a normal T4. Thyroid peroxidase and thyroglobulin antibodies show whether the immune system is attacking the thyroid, the cause of most thyroid disease in the UK. Together they tell you not just whether your thyroid is off, but why, and how it is likely to develop.

Thyroid peroxidase (TPO) and thyroglobulin (TG) are proteins inside the thyroid. Antibodies against them mean the immune system has identified the thyroid as a target: this is Hashimoto's thyroiditis when it leads to an underactive thyroid, and the same antibodies are often present in Graves' disease, the autoimmune cause of an overactive thyroid. Raised antibodies with a normal TSH mean you are at increased risk of developing thyroid disease, around 2 to 4 percent a year, and should have TSH checked annually. Raised antibodies with an abnormal TSH confirm the cause and mean the condition is likely to be permanent. Around one in ten healthy people has low-level antibodies without ever developing disease.

Anyone with a borderline or mildly raised TSH, because antibodies predict whether it will progress to needing treatment; anyone with a family history of thyroid disease or another autoimmune condition such as type 1 diabetes, coeliac disease or vitiligo; women planning a pregnancy or with recurrent miscarriage, since antibodies are linked to both and affect how TSH is managed in pregnancy; and anyone with persistent symptoms and a normal basic thyroid test who wants the fuller picture. If you have already been diagnosed and treated, antibodies rarely need repeating.

T4 is the hormone the thyroid releases; the body converts it to T3, which is the form that acts on cells. Most of the time free T4 tells the story, but when TSH is suppressed, free T3 distinguishes the types of overactive thyroid; when TSH is normal but symptoms persist, a low free T3 can point to poor conversion or to another cause entirely; and in people on treatment, T3 helps judge whether the dose is right. Adding it turns a screening test into a complete one.

Usually, in combination with the hormone results. Hashimoto's presents with a raised TSH, a low free T4 and, in about 90 percent of cases, raised TPO antibodies. Graves' disease presents with a low TSH and raised free T4 and free T3, often with TPO antibodies too; a specific TSH-receptor antibody test, which your GP can add, confirms it. Your GP report flags which results are outside the reference range and recommends the next step.

No fasting. Take the sample in the morning if you can, because TSH is highest early in the day. Stop biotin supplements, including hair, skin and nail formulas, for at least two days beforehand, as biotin interferes with the laboratory method and can make antibody and hormone results falsely abnormal. If you take levothyroxine, take the sample before your dose that day. Recent illness, pregnancy, steroids and amiodarone can all affect thyroid results.

The basic test (from £49) measures TSH, free T4 and free T3 and is available as a finger-prick kit; it answers whether your thyroid is working normally. This test (£109) adds the two antibodies and needs a venous sample; it answers why, and how likely a borderline result is to progress. If you have never been tested and have symptoms, the basic test is a sensible start. If your TSH has been borderline, you have a family history, you are planning a pregnancy, or you want the full picture once, choose this one.

Yes. Women with raised TPO antibodies have a higher rate of miscarriage and of developing an underactive thyroid during pregnancy, even when TSH is normal beforehand, and guidelines recommend closer TSH monitoring for them. Untreated hypothyroidism in pregnancy affects the baby's development, so knowing your antibody status before conceiving allows your GP or midwife to plan. This is one of the most useful reasons to have antibodies checked rather than TSH alone.

Your GP report interprets all five together. A raised TSH with low free T4 and positive antibodies is autoimmune hypothyroidism (Hashimoto's). A low TSH with raised free T4 and T3 is hyperthyroidism, autoimmune if antibodies are positive. Normal hormones with positive antibodies mean you are at risk and should be rechecked yearly. Normal hormones with negative antibodies make thyroid disease unlikely.

Take the GP report to your own GP. Hypothyroidism is treated with levothyroxine, a daily tablet that your GP prescribes and monitors, and most people feel much better within weeks. Hyperthyroidism is referred to an endocrinologist for treatment with tablets, radioactive iodine or occasionally surgery. Positive antibodies with normal hormones need no treatment, only annual monitoring, which our basic Thyroid Function test covers for £49.

Results are emailed within 3 to 5 working days of your sample reaching the laboratory, with a GP report that explains all five markers together and recommends the next step.

At any of 250+ Goodbody clinics across the UK, or with a nurse visiting your home. This test needs a venous sample so is not available as a finger-prick kit. No GP referral is needed. Find your nearest clinic.