Thyroid Disorders: Laboratory Diagnosis
The thyroid gland regulates metabolism, energy balance, cardiovascular function, and nervous system activity. Thyroid dysfunction is one of the most common endocrine disorders.
Key Biomarkers
| Biomarker | What It Shows | Normal Range |
|---|---|---|
| TSH | Pituitary–thyroid axis | 0.4–4.0 mIU/L |
| Free T4 | Active thyroid hormone | 10–23 pmol/L |
| Free T3 | Most active form | 3.1–6.8 pmol/L |
Hypothyroidism (Underactive Thyroid)
Lab pattern: TSH ↑, Free T4 ↓ (or normal in subclinical form)
Symptoms: fatigue, weight gain, cold intolerance, dry skin, constipation, bradycardia
Common causes: Hashimoto's thyroiditis, post-surgical, medication-induced
Hyperthyroidism (Overactive Thyroid)
Lab pattern: TSH ↓, Free T4 ↑ and/or Free T3 ↑
Symptoms: tachycardia, weight loss, tremor, sweating, irritability
Common causes: Graves' disease, toxic adenoma, thyroiditis
Testing Frequency
| Situation | Recommendation |
|---|---|
| Screening (no symptoms) | Every 5 years after age 35 |
| Levothyroxine dose adjustment | Every 6–8 weeks |
| Stable hypothyroidism | Every 6–12 months |
| Pregnancy | Every trimester |
FAQ
Is TSH alone sufficient?
For screening — yes. If TSH is abnormal, Free T4 and T3 should be tested to clarify the diagnosis.
Does food affect results?
TSH is best drawn fasting in the morning — levels have a circadian rhythm and may be lower after meals.
Track your thyroid markers with Lissa Health — charts help your doctor evaluate treatment effectiveness.