A thyroid blood test is one of the most requested blood tests. Your thyroid produces hormones that influence nearly every organ in your body. But which values are measured and when?
The three core values
TSH (0.4-4.0 mU/L) is the first and most important marker. Free T4 (12-22 pmol/L) is the main hormone your thyroid produces. Free T3 is the most active thyroid hormone, not always measured by default but useful when symptoms persist despite normal TSH and T4.
Additional markers
TPO antibodies (elevated in Hashimoto's) and TRAb (elevated in Graves' disease) are measured when investigating the cause of thyroid dysfunction.
When to test
Consider testing if you experience persistent fatigue, unexplained weight changes, feeling cold or overheating, mood changes, hair loss, palpitations or concentration problems. Thyroid problems are more common than you might think, especially in women over 35.
Frequently asked questions
Is thyroid tested in a standard blood test?
No, a thyroid test must be specifically requested. It is not included in routine GP blood work unless you ask for it or have symptoms.
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