Thyroid test for an underactive or overactive thyroid

Our thyroid sits at the front of the neck, just below the voice box. It makes two hormones: T4 and T3. These set your energy use, your heart rate and your body heat.

The working of the thyroid is driven from your brain. Your pituitary gland makes TSH. That is a stimulating hormone: it puts the thyroid to work.

This test reads three values. TSH shows how hard your pituitary is pulling on the thyroid. Free thyroxine, or free T4 for short, is the store hormone floating loose in your blood. Free T3 is the most active form.

A TSH value on its own does not tell the whole story. That is why we read the two hormones next to it.

Your thyroid can make too little hormone, or too much. Both cause symptoms, but very different ones.

With a slow working thyroid, output sits too low. Your energy use drops. Doctors call this hypothyroidism.

Common signs are tiredness, feeling cold, dry skin and weight gain. Low mood, hair loss and a slow gut also occur.

With a fast working thyroid the opposite happens. Everything speeds up. Think of a racing heart, sweating, unrest, poor sleep and weight loss. Doctors call this hyperthyroidism.

The blood picture differs clearly between the two. A slow thyroid tends to give a high TSH with a low free T4. A fast thyroid shows a low TSH instead.

Most thyroid problems in the Netherlands are not caused by diet or stress. They start with the immune system itself.

Hashimoto's disease is the best known. Here the body's own immune cells slowly damage the thyroid.

Hormone output falls over years. That is how a slow thyroid begins. Anti-TPO antibodies are often raised with it.

Graves' disease works the other way round. There, antibodies drive the thyroid into overwork. The result is a fast thyroid.

Both are far more common in women than in men. They also show up more often after birth and around menopause. This test does not read those antibodies itself.

In women, thyroid signs are often put down to something else. Tiredness, weight gain and mood swings also fit menopause. The two overlap a great deal.

That is exactly why a test helps here. You find out whether the thyroid plays a part or not.

Pregnancy is a different case. Your need for thyroid hormone rises in that period. The thyroid can also go off balance for a while after birth.

Are you pregnant or newly a mother? Then talk any off-range result through with your midwife or GP.

Do you know signs that could belong to the thyroid? Then this is a good first step. Think of long-running tiredness, weight change you cannot place, or mood swings.

Many women have these values read to gain insight into signs that have lasted months. The thyroid is also worth a look when you hope to get pregnant. It plays a part in fertility and in pregnancy.

Do you need more than these three values? If Hashimoto or Graves is in play, the antibodies belong in the picture too.

This test needs blood from a vein. You give your sample at a partner site near you. Those sites are run by independent, certified labs.

You usually do not need to fast. Many people give blood in the morning. Your values shift a little through the day, so this keeps results in step.

Do you take supplements with biotin? Those can throw the test off. Talk to the lab first.

Turnaround differs per test. For TSH we plan on roughly two days. For free T4 and free T3 we plan on roughly four days.

Your full result is ready once the last test is in. This is our planning guide, not a firm promise. Labs differ from one another in turnaround.

Every result comes with a review by a BIG-registered doctor.

You get each value back with the lab reference range next to it. Those ranges differ per lab. So always read the range printed on your own result.

Does a value sit just outside that range? That is not a diagnosis in itself. A single test stays a snapshot.

The doctor says whether more tests are needed. Sometimes that is just a repeat after a few weeks. Sometimes it is the antibodies, to rule Hashimoto or Graves in or out.

Always talk through treatment choices with your own GP.

Not every off-range value is clear cut. One well known picture is a mildly raised TSH with a normal free T4. Doctors call that subclinical.

A result like that rarely calls for treatment on its own. It does call for a repeat. TSH shifts from day to day, and even across the year.

So one test says little about a borderline case. A second test a few weeks later says far more. Put a result like that to your GP before you draw conclusions.