Low TSH means your pituitary gland is producing less thyroid-stimulating hormone than normal. This usually signals that your thyroid is overactive, though other factors can also play a role.
What Causes Low TSH?
- Hyperthyroidism: The most common cause — your thyroid makes too much hormone.
- Graves' disease: An autoimmune condition that overstimulates the thyroid.
- Thyroid nodules: Toxic nodules can produce excess thyroid hormone independently.
- Excess thyroid medication: Taking too much levothyroxine or other thyroid hormone.
- Pituitary dysfunction: Rarely, a problem with the pituitary itself.
Low TSH with Normal T4
This pattern is called subclinical hyperthyroidism. You may not have obvious symptoms, but it can increase the risk of heart problems and bone loss over time. Doctors usually monitor this closely and may treat it if TSH stays below 0.1 mIU/L.
Is Low TSH Dangerous?
Untreated low TSH can lead to irregular heartbeat, osteoporosis, anxiety, and eye problems (in Graves' disease). If you suspect low TSH, getting tested is the first step toward proper management.
Consider a Full Thyroid Panel
A TSH test screens for thyroid imbalance, but a complete thyroid panel adds Free T4, Free T3, and TSI antibodies — essential if hyperthyroidism or Graves' disease is suspected.
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