Thyroid Health11 min read
Guide to Testing Thyroid Biomarkers
How thyroid biomarkers connect to overall health — and why thyroid dysfunction affects approximately 12% of the population, with many cases going undiagnosed.
September 15, 2025Superpower Clinical TeamReviewed by Julija Rabcuka
Why Thyroid Dysfunction Matters
The thyroid regulates energy, growth, cardiovascular health, and brain development. Untreated hypothyroidism increases cardiovascular disease risk, while untreated hyperthyroidism raises the risk of atrial fibrillation and osteoporosis.
Systems Biology: The Thyroid's Connections
- Brain & Nervous System — essential for neurodevelopment; deficiency in infants can cause irreversible intellectual disability
- Cardiovascular System — regulates heart rate and cholesterol metabolism
- Liver & Metabolism — converts T4 to active T3 via deiodinase enzymes
- Reproductive System — affects menstrual regularity, fertility, and pregnancy outcomes
- Bone & Muscle — hyperthyroidism accelerates bone loss
- Immune System — autoimmune thyroid diseases cluster with other autoimmune conditions
Key Thyroid Biomarkers
Primary Markers
- TSH — first-line test; elevated indicates hypothyroidism
- Free T4 — main thyroid hormone; low with high TSH suggests primary hypothyroidism
- Free T3 — more potent hormone; helpful in diagnosing hyperthyroidism
- Reverse T3 (rT3) — inactive metabolite; limited routine diagnostic utility
Autoantibodies
- TPOAb — indicates Hashimoto's thyroiditis
- TgAb — frequently coexists with TPOAb
- TRAb/TSI — characteristic of Graves' disease
Reference Ranges
| Biomarker | Low | Normal | High | Meaning |
|---|---|---|---|---|
| TSH | < 0.4 | 0.4–4.0 | > 4.0 | Low = hyperthyroidism; High = hypothyroidism |
| Free T4 | < 0.8 | 0.8–1.8 | > 1.8 | Low = hypothyroidism; High = hyperthyroidism |
| Free T3 | < 2.3 | 2.3–4.2 | > 4.2 | Low = conversion impairment; High = hyperthyroidism |
Supporting Healthy Thyroid Function
Nutrition
- Iodine — required for hormone synthesis
- Selenium — supports deiodinase activity and T4-to-T3 conversion
- Iron and zinc — necessary cofactors for thyroid enzyme function
Lifestyle
- Regular physical activity supports metabolic rate
- Adequate sleep and stress management reduce cortisol interference
- Limiting endocrine-disrupting chemical exposure protects thyroid signaling
Who Should Test?
Thyroid biomarkers are particularly valuable for women of reproductive age, older adults, those with unexplained cardiovascular findings, and patients with autoimmune disease. Comprehensive testing — including TSH, free T4, free T3, and antibodies — provides a systems-level view of thyroid health integrated with metabolic and cardiovascular data.