Normal blood thyroid levels
Normal thyroid blood tests
- TSH: 0.5 – 5.0 mU/L. This is the most important test. High or low TSH levels can indicate a thyroid problem
- Free thyroxine (T4): 8.0 – 18.0 pmol/L
- Free triiodothyronine (T): 3.8 – 6.0 pmol/L.
Explanation
- Low TSH and high thyroxine (T4): may indicate an overactive thyroid gland (hyperthyroidism)
- High TSH and low thyroxine (T4): may indicate an underactive thyroid gland (hypothyroidism)
- 5-10 mU/L is mild hypothyroidism; >10 mU/L is hypothyroidism
- TSH levels can vary depending on the laboratory that tested the sample – and other factors including age, gender, pregnancy and overall health
- Various drugs also affect TSH levels (Amiodarone, Dopamine, Lithium, Potassium iodide and steroids like Prednisolone)
Note 1. If your test results show raised TSH but normal T4, you may be at risk of developing an underactive thyroid in the future. This may or may not need to be treated
Note 2. There is a less prominent hormone called calcitonin that your thyroid gland produces. It helps regulate calcium and phosphate levels in your blood, contributing to healthy bones. This is not normally measured.
Other specialist thyroid tests
Doctors may also check for thyroid antibodies, including:
- Thyroid peroxidase antibodies (TPO), which can be a sign of Hashimoto disease or Graves’ disease (both causes of an overactive thyroid gland)
- Thyroglobulin antibodies (Tg), which can be a sign of Hashimoto disease
- TSH receptor antibodies (TSHR Ab, also known as TRAb), which can be a sign of Graves’ disease.
What is the thyroid gland?
The thyroid is a butterfly-shaped gland in the front of the neck that produces hormones that regulate metabolism, heart rate, and other bodily functions. You cannot feel the thyroid gland, as it is quite flat.
What does it do?
Thyroid-stimulating hormone (TSH) is made by the pituitary gland, a small gland right at the base of the brain). It controls the levels of triiodothyronine (T3) and thyroxine (T4) hormones in the blood.
Both T3 and T4 are made by the thyroid gland. Hormones are chemical messengers.
Why does it matter?
Thyroid disease is very common. 1 in 8 females experience thyroid problems at some point. This includes hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid).
Summary
We have described what are normal blood thyroid levels. We hope it has been helpful.
