Your thyroid is a small butterfly-shaped gland in your neck, but it controls your metabolism, energy, weight, mood, and temperature. Thyroid blood tests help reveal whether it's working too hard, too little, or just right.
The Key Thyroid Tests
- TSH (Thyroid Stimulating Hormone) — produced by the pituitary gland to tell the thyroid how much hormone to make. It's the most sensitive first-line test.
- Free T4 — the main hormone the thyroid releases, mostly inactive until converted.
- Free T3 — the active hormone that drives your metabolism.
- Anti-TPO antibodies — markers of autoimmune thyroid disease such as Hashimoto's.
Reading the Pattern
TSH works like a thermostat, so it often moves opposite to the thyroid hormones:
- High TSH + low T4 — an underactive thyroid (hypothyroidism): fatigue, weight gain, feeling cold, dry skin, low mood.
- Low TSH + high T4/T3 — an overactive thyroid (hyperthyroidism): palpitations, weight loss, anxiety, heat intolerance.
- Mildly high TSH with normal T4 — subclinical hypothyroidism, which your doctor may monitor or treat depending on symptoms.
Why Thyroid Problems Are So Common
Thyroid disorders are widespread, particularly in women and after pregnancy. Many people have symptoms for years before being tested, which is why a simple TSH check is so valuable when you feel persistently tired, gain or lose weight unexpectedly, or notice mood changes.
When to See Your Doctor
Bring your results to a doctor if your TSH is outside range, if you have a goiter (neck swelling), or if antibody levels are high. Thyroid conditions are very treatable — usually with a once-daily tablet and periodic monitoring.
Decode Your Thyroid Panel
Upload your thyroid report to Lab Lens to see exactly what your TSH, T3, and T4 results mean in plain language.