TRAb: what they are, what they tell you and when they’re tested

TRAb are antibodies against the TSH receptor, a kind of lock that TSH opens to make your thyroid work. In Graves’ disease these antibodies turn the key instead of TSH, and the thyroid works too hard. They are the test that recognises it.

When they’re tested

Doctors order them when the thyroid is working too hard, with a low TSH and a high FT4 or FT3, to see whether Graves’ disease or something else is the cause.

They also order them before stopping thyroid medicines, because they help show whether Graves’ disease may come back, and in pregnancy in women who have or have had Graves’. Sometimes they order them for eye problems typical of Graves’.

They are not needed if your thyroid works well. That is why Rosa does not test them. Rosa measures TSH, the first test to fall when the thyroid works too hard.

What they tell you, and what they do not

If they are positive and the thyroid is working too hard, it is almost always Graves’ disease. If they are negative, your doctor looks for other causes, such as a nodule or thyroiditis.

They do not say how much the thyroid is working: TSH, FT4 and FT3 tell you that. And a positive value on its own, with a thyroid that works well, should be read with your doctor.

During treatment, if they fall until they turn negative, Graves’ disease is less likely to come back when the medicines are stopped.

That is why they are read together with other tests:

Normal TRAb levels

Your report usually says whether they are negative or positive, above a limit the lab sets. Different methods exist, and the limit varies between them: the one on your report is what counts.

In people without thyroid disease they are negative. To follow them over time, for example during treatment, it is best to have them done at the same lab.

If your TRAb are positive or negative

Positive TRAb: what it means

The most common situations:

Symptoms of Graves’ disease

TRAb themselves cause no symptoms. The overactive thyroid does, and sometimes the eyes:

If you have these symptoms, talk to your doctor: Graves’ disease is very treatable, and the sooner treatment starts the better.

TRAb and your eyes

In Graves’ disease the antibodies can also affect the tissues behind the eyes. The eyes can bulge, turn red, and sometimes you see double.

Smoking is the biggest risk you can change: people who smoke have eye problems more often, and worse ones. If you smoke, stopping protects your eyes.

If you have eye problems, your doctor usually refers you to a specialist centre. If your sight gets worse or colours look duller, it is an emergency.

What can skew the result

Only a few things, but they are worth knowing.

When to worry

Talk to your doctor if:

Frequently asked questions

What are normal TRAb levels? It depends on the lab. Your report gives a limit: below it is negative, above it is positive. In people without thyroid disease they are negative.

Do positive TRAb mean Graves’ disease? If the thyroid is working too hard, almost always yes. The diagnosis is made by your doctor, though, with TSH, FT4, sometimes an ultrasound and an examination.

Can TRAb turn negative? Yes. With treatment they often fall slowly, over months. If they turn negative, Graves’ disease is less likely to come back when the medicines are stopped. Your endocrinologist decides.

Why are TRAb measured in pregnancy? Because they can cross the placenta and act on the baby’s thyroid. That is why, in women who have or have had Graves’ disease, the obstetrician and endocrinologist check them.

Does Rosa test TRAb? No. Rosa measures TSH, which falls when the thyroid works too hard. If your doctor wants TRAb, they order them separately.

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