What Is TSH in a Blood Test?
TSH is produced by the pituitary gland and tells your thyroid how much hormone to produce.
Normal Range
- 0.4–4.0 mIU/L
What It Means
- High TSH = hypothyroidism (underactive thyroid)
- Low TSH = hyperthyroidism (overactive thyroid)
- Normal TSH usually rules out thyroid dysfunction
Why TSH Is the Best Screening Test
- Changes occur early, before T4 falls outside range
- Logarithmic changes make it highly sensitive
Source: NLM MedlinePlus, American Association for Clinical Chemistry.
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