Thyroid test: a small gland with big effects

The thyroid is a small gland in the neck that controls how fast your body uses energy. Thyroid problems are common, especially in women, and can go unnoticed for years because the symptoms develop slowly.

Signs that it may be worth checking

• Tiredness, weakness or low mood
• Weight gain or weight loss without a clear reason
• Hair fall, dry skin or brittle nails
• Feeling unusually cold or unusually hot
• Irregular or heavy periods, or difficulty conceiving
• A racing heartbeat, tremor or anxiety
• A swelling in the front of the neck

Which tests are done?

• TSH — the signal from the brain that tells the thyroid to work. It is usually the first and most sensitive test.
• T3 and T4 (or free T4) — the thyroid hormones themselves.
• Anti-TPO antibodies — sometimes added to look for autoimmune thyroid disease.

A high TSH usually suggests an underactive thyroid (hypothyroidism); a low TSH may suggest an overactive thyroid (hyperthyroidism). Your doctor will interpret the results together with your symptoms.

Thyroid and pregnancy

Thyroid levels are especially important before and during pregnancy, because they affect the baby's development. Many doctors check TSH early in pregnancy or when planning one.

Do I need to fast?

Fasting is usually not needed. If you take thyroid medicine, ask your doctor whether to give the sample before your morning dose.