THYROXINE-BINDING GLOBULIN TEST ( TBG )
Reports in 7 DAYS
🧪 Thyroxine-Binding Globulin (TBG) Test The Thyroxine-Binding Globulin (TBG) test measures the amount of TBG protein in your blood. TBG is a transport protein that binds to thyroid hormones (T3 and T4) and carries them through the bloodstream. It’s not a routine thyroid function test, but it’s useful in special cases when thyroid hormone levels seem abnormal but TSH, Free T3, and Free T4 don’t fully explain symptoms. 🧬 What Is TBG? Feature Description Full Name Thyroxine-Binding Globulin Main Role Binds to and transports T3 and T4 Bound Hormones Are inactive (only free hormones are active) Produced by Liver 📊 Normal Reference Range (May vary by lab) Test Normal Range TBG 15 – 30 µg/mL (or) 1.3 – 2.0 mg/L 📈 High or 📉 Low TBG – What It Means 📈 Increased TBG More hormone is bound, less Free T4/T3 available (but Total T4/T3 may be high) Causes: Pregnancy (due to estrogen) Estrogen therapy (e.g., oral contraceptives) Hepatitis Genetic increase in TBG 📉 Decreased TBG Less hormone is bound, more Free T4/T3 relative to Total Causes: Liver disease Nephrotic syndrome Corticosteroid use Androgens or anabolic steroids Genetic TBG deficiency 🧪 Why Is the TBG Test Done? Use Case Purpose Unexplained high or low Total T4/T3 To assess if altered due to binding issues Pregnancy or hormone therapy Understand changes in thyroid tests Suspected inherited TBG disorder Evaluate genetic binding protein conditions 🧾 Example Lab Report Test Result Reference Range Thyroxine-Binding Globulin 28 µg/mL 15 – 30 µg/mL ✅ Interpretation: TBG within normal limits — does not affect total/free T3/T4 interpretation. 🧠 Important Notes TBG does not measure thyroid hormone levels directly. Use Free T3 and Free T4 to assess actual thyroid hormone activity. If Total T4 is high and Free T4 is normal, elevated TBG might be the reason. ✅ Summary Feature Details Test Thyroxine-Binding Globulin (TBG) Function Binds and transports thyroid hormones High TBG Seen in pregnancy, estrogen therapy Low TBG Seen in liver disease, steroid use Best Used With Total and Free T4/T3 levels





























