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