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🧪 What is Total Thyroxine (T4)?

Total Thyroxine (T4) measures the total amount of thyroxine hormone in the blood, including both bound (to proteins like thyroxine-binding globulin) and free (unbound, biologically active) forms. T4 is produced by the thyroid gland and is a key hormone regulating metabolism.

❓ Why is the Test Done?

To:

Evaluate thyroid function and diagnose thyroid disorders such as hypothyroidism or hyperthyroidism
Monitor treatment of thyroid diseases
Assess thyroid status during pregnancy or other clinical situations
Complement other thyroid tests like TSH and Free T4

📊 Normal Range

Total T4 Level	Reference Range
Adults	5.0 – 12.0 µg/dL (64 – 154 nmol/L)

Normal ranges may vary slightly depending on laboratory methods.

📈 Interpretation of Results

Result	Clinical Significance
High Total T4	Hyperthyroidism, thyroid hormone replacement therapy, thyroiditis
Low Total T4	Hypothyroidism, iodine deficiency, pituitary disease
Normal Total T4	Normal thyroid function or compensated disorders

🧠 Associated Conditions

Condition	Details
Hyperthyroidism	Graves’ disease, toxic nodular goiter
Hypothyroidism	Hashimoto’s thyroiditis, iodine deficiency
Thyroid hormone therapy	Monitoring of replacement doses
Pregnancy	Increased thyroid binding globulin can alter total T4

🔄 Related / Follow-Up Tests

Thyroid Stimulating Hormone (TSH)
Free T4 (Free Thyroxine)
Free T3 (Triiodothyronine)
Thyroid autoantibodies

✅ Fasting Required?

Test	Fasting Required
Total Thyroxine (T4)	❌ No

📝 Summary Table

Parameter	Details
What	Measures total thyroxine hormone (bound + free)
Why	Assess thyroid function and monitor thyroid diseases
Normal Range	5.0 – 12.0 µg/dL
High Levels	Hyperthyroidism, thyroid hormone therapy
Low Levels	Hypothyroidism, iodine deficiency
Associated Conditions	Thyroid dysfunction, thyroiditis, pregnancy
Follow-up Tests	TSH, Free T4, Free T3, thyroid antibodies
Fasting Required	❌ No

Total Thyroxine (T4)

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