Understanding Thyroid Tests
Your thyroid is a small gland that has a huge impact on your metabolism, energy, weight, and overall health. Thyroid function tests help identify if your thyroid is working properly.
The Three Main Thyroid Tests
TSH (Thyroid Stimulating Hormone)
Normal range: 0.4 - 4.0 mIU/L
TSH is produced by your pituitary gland and tells your thyroid how much thyroid hormone to make. It's usually the first thyroid test ordered.
Free T4 (Thyroxine)
Normal range: 0.8 - 1.8 ng/dL
T4 is the main hormone your thyroid produces. Most T4 is bound to proteins, but "free" T4 is the active form.
Free T3 (Triiodothyronine)
Normal range: 2.3 - 4.2 pg/mL
T3 is the most active thyroid hormone. Your body converts T4 into T3.
What High TSH Means (Hypothyroidism)
High TSH with low T4 indicates an underactive thyroid. Symptoms include:
- Fatigue and weakness
- Weight gain
- Cold sensitivity
- Depression
- Dry skin and hair loss
What Low TSH Means (Hyperthyroidism)
Low TSH with high T4 indicates an overactive thyroid. Symptoms include:
- Unexplained weight loss
- Rapid heartbeat
- Anxiety and irritability
- Heat sensitivity
- Tremors
Check Your Thyroid Results
Use our free thyroid test interpreter to understand your TSH and thyroid hormone levels.
Note: Always discuss thyroid test results with your healthcare provider for proper diagnosis and treatment.