1. Introduction to Thyroxine-Binding Globulin (TBG)

What is Thyroxine-Binding Globulin (TBG)? Thyroxine-Binding Globulin (TBG) is a liver-produced plasma protein that binds and transports thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), in the bloodstream. It plays a critical role in regulating the availability of thyroid hormones to tissues. Measuring TBG levels in blood helps evaluate discrepancies in thyroid function tests, particularly when Total T4 or T3 levels are abnormal, and diagnose conditions affecting thyroid hormone binding, such as TBG deficiency or excess.

2. What is a TBG Unit Converter?

Definition: The TBG Unit Converter converts TBG concentrations between various units, enabling standardization of laboratory results for clinical use.

Purpose: It assists clinicians and researchers in interpreting TBG levels across different measurement units (e.g., nmol/L to mg/L), ensuring accurate assessment of thyroid hormone binding and related disorders.

3. Importance of TBG Unit Conversions

Converting TBG concentrations between units is critical for:

• Standardizing Results: Different labs report TBG in various units (e.g., nmol/L, mg/L); conversion ensures consistency for diagnosis.
• Clinical Diagnosis: Accurate conversions aid in diagnosing TBG deficiency or excess, interpreting thyroid function tests, and managing thyroid disorders.
• Research and Collaboration: Enables comparison of TBG data across studies or institutions using different measurement standards.

4. Clinical Significance

Elevated Levels: High TBG levels increase Total T4 and T3 without affecting free hormone levels, often seen in pregnancy, estrogen therapy, liver disease (e.g., hepatitis), or genetic TBG excess. This can lead to misinterpretation of thyroid function tests if not recognized.

Low Levels: Low TBG levels decrease Total T4 and T3, seen in TBG deficiency (genetic or acquired), liver failure, nephrotic syndrome, or androgen use. This may mimic hypothyroidism if only Total T4 is measured.

Normal Ranges:

• Typically 16–36 mg/L (1.6–3.6 mg/dL or 260–600 nmol/L).
• Values vary by lab, sex, and assay—consult a healthcare provider for interpretation.

5. Precautions

Interferences:

• TBG levels are influenced by estrogen, liver function, medications (e.g., tamoxifen, anabolic steroids), and genetic variations.
• TBG measurement is most useful when combined with Total T4, free T4, TSH, and clinical findings to differentiate binding protein abnormalities from true thyroid dysfunction.
• Sample handling (e.g., avoiding hemolysis, timely processing) is critical for accurate results—consult a healthcare provider for accuracy.

6. Frequently Asked Questions (FAQ)

Q: Why are there different units for TBG?
A: Different units reflect varying standards; nmol/L is the SI unit, while mg/L and mg/dL are commonly used in clinical practice, particularly in different regions.

Q: What is a normal TBG level?
A: Normal TBG is typically 16–36 mg/L (1.6–3.6 mg/dL or 260–600 nmol/L). Consult a healthcare provider for interpretation.

Q: Can this converter be used for other binding proteins?
A: No, this converter is specific to TBG; other binding proteins (e.g., albumin, sex hormone-binding globulin) have different units and conversion factors—consult a healthcare provider for accuracy.