🧠 Thyroid Profile – Total T3, Total T4 & TSH

1. TSH (Thyroid Stimulating Hormone)

• ✅ Fasting: Preferred (morning sample recommended)
• 🎯 Produced by: Pituitary gland
• 📊 Measures: The signal sent from the pituitary to the thyroid to release hormones
• 📈 High TSH: Indicates hypothyroidism (underactive thyroid) – thyroid not responding well
• 📉 Low TSH: Indicates hyperthyroidism (overactive thyroid) – too much hormone circulating
• ✅ Normal Range: 0.4 – 4.0 mIU/L (can vary slightly by lab)
• 🩺 Most sensitive indicator of thyroid dysfunction

2. Total T4 (Thyroxine)

• ✅ Fasting: Yes (8–10 hrs recommended)
• 🎯 Produced by: Thyroid gland
• 📊 Measures: Total amount of thyroxine (bound + unbound/free) in blood
• 📈 High T4: Hyperthyroidism, thyroiditis, thyroid hormone overdose
• 📉 Low T4: Hypothyroidism, pituitary dysfunction
• ✅ Normal Range: 5 – 12 µg/dL
• 🩺 Used with TSH to confirm diagnosis of thyroid disease

3. Total T3 (Triiodothyronine)

• ✅ Fasting: Yes
• 🎯 Produced by: Thyroid (and converted in liver from T4)
• 📊 Measures: Total amount of T3 (bound + unbound)
• 📈 High T3: T3 toxicosis, Graves’ disease, hyperthyroidism
• 📉 Low T3: Hypothyroidism, chronic illness (non-thyroidal illness syndrome)
• ✅ Normal Range: 80 – 200 ng/dL
• 🩺 More specific for diagnosing early hyperthyroidism

🔁 Thyroid Hormone Regulation Flowchart

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Pituitary (brain)

↓ (secretes TSH)

Thyroid Gland

↓ (produces T4 → converted to T3)

Body Metabolism Regulated

If T3/T4 are low, the pituitary makes more TSH (↑ TSH).
If T3/T4 are high, the pituitary reduces TSH (↓ TSH).

🧪 When Is This Profile Ordered?

• Symptoms of hypothyroidism: Fatigue, weight gain, cold intolerance, constipation, dry skin, depression
• Symptoms of hyperthyroidism: Weight loss, palpitations, heat intolerance, anxiety, insomnia, tremors
• Routine screening in adults, pregnant women, and people with autoimmune disease
• Monitoring after thyroid surgery, medication, or radioactive iodine therapy

🔄 Common Associated Tests

📊 Interpretation Matrix