Thyroid Tests: Types and What They Show

For many people, checking the thyroid is associated with a single test: take it and the picture is clear. In reality, this is several different tests, and each answers its own question. We explain what thyroid tests exist and where to start with testing.

When the thyroid is checked

The thyroid gland is a small butterfly-shaped gland in the front of the neck. It produces hormones that control how the body uses energy and affect breathing, heart rate, weight, digestion and mood. Tests show how well it is working and help find the cause of diseases such as hyperthyroidism and hypothyroidism.

The reason to check the gland is often symptoms of reduced function: pronounced fatigue, feeling colder than usual, weight gain, constipation, difficulty concentrating, low mood, dry skin, dry hair or hair loss, a hoarse voice, irregular or heavy periods. They develop slowly and worsen over time, and many of them also occur in other conditions.

The doctor asks about symptoms, about thyroid and autoimmune diseases in relatives, about a recent pregnancy, may palpate the neck and order blood tests, and if necessary refer you to a specialist.

What thyroid hormone tests exist

The laboratory part is a blood test, and it usually includes several markers.

• TSH — thyroid-stimulating hormone, as a rule the first test the doctor orders;
• T3 and T4 — the levels of different thyroid hormones in the blood;
• thyroid antibodies — blood markers that help diagnose autoimmune diseases;
• calcitonin — a peptide hormone of the gland's C cells, involved in phosphorus-calcium metabolism.

TSH, T3 and T4: what each marker is responsible for

T4 and T3 are iodinated tyrosine derivatives that differ in the number of iodine atoms in the molecule but share common properties. Per day the gland produces approximately 80–100 mcg of thyroxine (T4). In the blood both hormones exist in free and protein-bound forms, and only the free fractions — fT4 and fT3 — are active.

Thyroid hormones suppress TSH secretion, so its level is used to judge how the system is working.

Antibodies and tests for thyroiditis

An antibody test measures certain antibodies in the blood and helps diagnose autoimmune diseases of the gland. In thyroiditis this is a way to find the cause: in Hashimoto's disease the immune system attacks the gland, and it cannot produce enough hormones. Hashimoto's is more common in women and usually begins between the ages of 30 and 50.

Other causes include surgery or radiation therapy to the neck, treatment of hyperthyroidism, iodine deficiency, and certain medications. If relatives have had thyroid disease, the risk is higher.

Other examination methods: palpation and ultrasound

Thyroid palpation is feeling the neck: the doctor assesses whether the gland is enlarged.

Imaging methods include ultrasound, computed tomography and studies with radioactive substances. A thyroid scan with a small amount of radioactive material shows its size, shape and position, helps find the cause of hyperthyroidism and check nodules. A radioactive iodine uptake test shows how well the gland is working.

How to read the results and when to see a doctor

Looking at the report by a single marker is pointless: TSH usually comes first, T4 complements it, antibodies explain the cause, and ultrasound and scanning add to the picture of the structure. An abnormality is a reason to talk to a doctor, not a ready-made diagnosis.

You should see a doctor if symptoms of reduced function appear, especially several and worsening, if relatives have had thyroid or autoimmune diseases, if you are pregnant or planning a pregnancy. Untreated hypothyroidism is associated with an increased risk of heart problems, including coronary artery disease and heart failure, and of bone problems, including osteoporosis.

During pregnancy additional tests will be needed, and untreated hypothyroidism increases the risk of preeclampsia, birth defects, preterm birth and miscarriage — this conversation with a doctor is best not delayed.

Thyroid testing by itself is not a reason to call an ambulance. 103 or 112 — if a person with severe hypothyroidism, more often an older person, sharply deteriorates: in rare cases myxedema coma develops, a life-threatening condition treated in hospital.

This material is for reference and does not replace a doctor's consultation: discuss the numbers in the report with your doctor, not with a search engine.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer