Thyroid Tests: TSH, T3 and T4 — What They Mean
TSH is the control signal, T3 and T4 are the thyroid hormones. A change in one without the others still needs a doctor’s reading.
TSH, T3, T4 in plain words
Your pituitary gland sends TSH to tell the thyroid to work. The thyroid then makes T4, which the body converts to the active hormone T3.
- High TSH with low T4 often points to an underactive thyroid.
- Low TSH with high T4 often points to an overactive thyroid.
These are patterns, not diagnoses. Medicines, pregnancy, illness and lab variation can all affect results.
When to test
Common reasons include unexplained weight change, tiredness, hair loss, irregular periods, or a family history of thyroid disease. Your doctor can advise whether and how often to test.
Disclaimer: This article is general health information only, not medical advice. Consult a doctor for personal health decisions, symptoms, or test results.
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