What Thyroid Labs Measure
Think of your thyroid as the thermostat of your body. It helps regulate temperature, metabolism, energy, weight, mood, and even your hair and skin.
When doctors order thyroid labs, they’re checking in on how that thermostat is working. The four most common tests are:
TSH (Thyroid Stimulating Hormone)
Free T4
Free T3
Thyroid Antibodies (TPO, TgAb, TSI)
Each one tells a slightly different story about thyroid health.
Why These Labs Matter
The thyroid plays a role in nearly every system in your body. When it’s underactive (hypothyroidism), you may feel fatigued, gain weight easily, feel depressed, or notice hair loss and dry skin. When it’s overactive (hyperthyroidism), you may lose weight unexpectedly, feel anxious, have a racing heart, or struggle with insomnia.
Antibody testing is especially important because it can uncover autoimmune thyroid conditions such as Hashimoto’s (the most common cause of hypothyroidism) or Graves’ disease (a cause of hyperthyroidism).
That’s why looking beyond just TSH — the one test most doctors rely on — matters.
Breaking Down the Numbers
TSH (Thyroid Stimulating Hormone)
Think of TSH as the text message from your brain to your thyroid.
High TSH: Your brain is shouting louder, trying to get your thyroid to make more hormone → often points to hypothyroidism.
Low TSH: Your brain doesn’t need to send many messages because your thyroid is making too much → often points to hyperthyroidism.
Free T4
This is the storage form of thyroid hormone — the hormone your thyroid produces and releases into circulation.
Free T3
This is the active thyroid hormone — the one that actually enters your cells and powers metabolism, energy, and brain function.
If Free T3 is low (even with normal T4), you may feel hypothyroid.
Poor conversion of T4 → T3 can happen with stress, illness, or nutrient deficiencies.
Thyroid Antibodies
These are immune system markers that show whether your body is attacking your thyroid.
TPO antibodies (thyroid peroxidase): Common in Hashimoto’s.
TgAb (thyroglobulin antibodies): Another marker of autoimmune activity.
TSI (thyroid stimulating immunoglobulins): Linked to Graves’ disease.
📊 Standard Ranges vs. Optimal Ranges
TSH “normal” lab range: ~0.5–4.5 mIU/L.
Functional medicine often considers optimal ~1–2.5 mIU/L (especially if symptomatic).
Free T4/T3 ranges vary, but “low-normal” with symptoms can still suggest dysfunction.
Factors That Affect Thyroid Labs
Your thyroid results aren’t only about diet. Many factors can shift your numbers:
Stress + cortisol: Can block T4 → T3 conversion.
Nutrient deficiencies: Low iodine, selenium, zinc, iron.
Medications: Steroids, birth control, lithium.
Inflammation + illness: Temporary changes can happen during infections.
Autoimmune activity: Antibodies can rise years before symptoms show.
Supporting Healthy Thyroid Function (Non-Prescriptive Tips)
While everyone’s thyroid journey is different, here are general ways to support thyroid health naturally:
🥩 Nutrient-dense foods rich in selenium (Brazil nuts, eggs), zinc (meat, pumpkin seeds), and iron.
🥗 Balanced meals with protein, fiber, and healthy fats for blood sugar support.
🛌 Prioritize sleep — your thyroid needs rest to regulate metabolism.
🧘 Stress management — meditation, walks, or journaling to keep cortisol in check.
🚶 Gentle movement — walking, yoga, strength training to support metabolism.
🌱 Support gut health — much of thyroid conversion happens in the gut.
Testing Options
If you want to track your thyroid health between doctor visits, at-home test bundles can give you insight without the wait. Here are a few trusted options I recommend:
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Next Steps
Your labs are only part of the story. Understanding your symptoms, habits, and daily stressors is just as important.
✨ Book your free 60-min consultation with me — I’ll help you connect your numbers with your real-life health.
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