What Your Thyroid Does
Your thyroid is a small, butterfly-shaped gland in your neck that produces hormones controlling your metabolism — how your body uses energy. When it makes too much or too little hormone, it affects nearly every system in your body, from your heart rate to your mood.
The Key Tests
TSH (Thyroid-Stimulating Hormone) This is the most important screening test. TSH comes from your pituitary gland and tells your thyroid how much hormone to make. Counterintuitively, a **high** TSH usually means an **underactive** thyroid (the body is shouting for more hormone), while a **low** TSH suggests an **overactive** thyroid.
Free T4 and Free T3 These measure the actual thyroid hormones circulating in your blood. They help confirm and clarify what the TSH is hinting at.
What the Patterns Mean
| Pattern | Likely meaning |
|---|---|
| High TSH, low T4 | Underactive thyroid (hypothyroidism) |
| Low TSH, high T4/T3 | Overactive thyroid (hyperthyroidism) |
| Mildly high TSH, normal T4 | Subclinical hypothyroidism (often monitored) |
Reference ranges vary slightly between labs, so always read your result against the range printed on your own report.
Symptoms to Connect the Dots
Underactive (hypothyroidism): fatigue, weight gain, feeling cold, dry skin, constipation, low mood.
Overactive (hyperthyroidism): weight loss, rapid heartbeat, anxiety, feeling hot, trembling hands, trouble sleeping.
What Happens Next
- **Hypothyroidism** is usually treated with a daily thyroid hormone replacement pill, with periodic TSH checks to fine-tune the dose.
- **Hyperthyroidism** has several treatment paths and is often managed with a specialist (endocrinologist).
- **Borderline results** are often simply re-tested in a few weeks or months before any treatment.
Talk to Your Doctor
A single out-of-range value doesn't always mean a problem — thyroid levels can shift with illness, pregnancy, and certain medications. Your doctor interprets the numbers alongside your symptoms and history.
This article is for informational purposes only and does not constitute medical advice. Always consult a licensed Canadian healthcare professional.
