What Does Your Thyroid Do?
Your thyroid is a small, butterfly-shaped gland at the base of your neck. It produces hormones that regulate your metabolism — the process by which your body converts food into energy. Thyroid hormones affect virtually every cell in your body: heart rate, body temperature, weight, energy levels, mood, digestion, and even how quickly you think.
Key Thyroid Markers
A thyroid panel typically includes these tests.
- TSH (Thyroid Stimulating Hormone) — Usually the first test ordered. Normal: 0.4–4.0 mIU/L. High TSH = underactive thyroid; low TSH = overactive.
- Free T4 (Thyroxine) — The main thyroid hormone. Normal: 0.8–1.8 ng/dL.
- Free T3 (Triiodothyronine) — The more active thyroid hormone. Normal: 2.3–4.2 pg/mL.
- Thyroid Antibodies (TPO, TgAb) — Help detect autoimmune thyroid conditions.
Hypothyroidism (Underactive Thyroid)
Hypothyroidism occurs when your thyroid does not produce enough hormones. It is the most common thyroid disorder, affecting about 5% of adults. Lab results typically show high TSH with low Free T4.
- Symptoms: fatigue, weight gain, feeling cold, dry skin, constipation, depression, brain fog.
- Most common cause: Hashimoto's thyroiditis (autoimmune).
- Treatment: thyroid hormone replacement medication.
Hyperthyroidism (Overactive Thyroid)
Hyperthyroidism occurs when your thyroid produces too much hormone. Lab results typically show low TSH with high Free T4 or Free T3.
- Symptoms: weight loss, rapid heartbeat, anxiety, tremors, heat intolerance.
- Most common cause: Graves' disease (autoimmune).
- Treatment options: medication, radioactive iodine therapy, or surgery.
When to Get Your Thyroid Checked
Consider asking your doctor about thyroid testing if you experience unexplained fatigue, weight changes, or mood changes. Routine screening is recommended for women over 35, anyone with a family history of thyroid disease, pregnant women, and people with other autoimmune conditions. Tracking your thyroid levels over time is especially important if you are on thyroid medication, as dosing adjustments are common.
Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions about your health or lab results. Do not disregard professional medical advice or delay seeking it because of something you have read here.