T4 Lab Test
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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)
See Also | Lab Tests |
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Thyroxine or T4 is the major hormone secreted by the thyroid gland. The production and secretion of T4 from the thyroid gland is stimulated by TSH or thyroid-stimulating hormone. T4 consists of a tyrosine molecule with 4 iodine atoms attached to it. The active thyroid hormone T3 is formed from the cleavage of an iodine molecule from T4. The majority of T4 is transported through the blood by being bound to thyroxine-binding globulin (TBG), pre-albumin, and albumin.[1],[2]
Discussion
- T4 conversion into T3 is dependent upon the presence of iodine, selenium, and tyrosine amongst other nutrients
- Thyroxine has a wide range of metabolic activities in the body:
Patient Preparation
- No fasting is required
- Factors which can cause increased levels
- Factos which can cause decreased levels: None noted
- Drugs: Steroids, androgens, danazol, phenytoin, and propanolol
Clinical Implications
Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]
Standard U.S. Units | Standard International Units | |
---|---|---|
Conventional Laboratory Range | 4.8-13.2 mcg/dL | 61.8-169.9 mmol/L |
Optimal Range | 6.0-12.0 mcg/dL | 77.2- 154.4 mmol/L |
Alarm Ranges | <5.0 or > 13.0 mcg/dL | <65 or > 167 nmol/L |
High levels indicate:
- Hyperthyroidism
- Thyroid hormone replacement
- other conditions: liver disease (cirrhosis), elevated metabolic activity, pregnancy, adrenal fatigue
Low levels indicate:
- Primary hypothyroidism
- Iodine deficiency
- Steroid usage
- Other conditions: chronic liver disease, protein malnutrition, nephrosis
Associated Tests
- Serum T-3 uptake, T-3, free thyroxine index (FTI), thyroid stimulating hormone (TSH), thyroid binding globulin (TBG), serum triglycerides, serum cholesterol, serum calcium, serum phosphorous, RBC magnesium, serum albumin, HCT, HGB
References
- ↑ Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
- ↑ 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain