Thyroxine (T4) Free Thyroid Blood Test

Why is this test important?  This thyroid function blood test measures the amount of thyroxine, or T4, in your blood. T4 is one of two major hormones produced by the thyroid gland (the other is called triiodothyronine, or T3).

The body has a feedback system that turns thyroid hormone production on and off. When the level of T4 in the bloodstream decreases, the hypothalamus (an organ in the brain) releases thyrotropin releasing hormone, which stimulates the pituitary gland (an organ below the hypothalamus) to release thyroid-stimulating hormone (TSH), which in turn stimulates the thyroid gland to make and/or release more T4. As blood concentrations of T4 increase, TSH release is inhibited.

If the thyroid gland does not produce sufficient T4, due to thyroid dysfunction or to insufficient TSH, then the affected patient experiences symptoms of hypothyroidism such as weight gain, dry skin, cold intolerance, irregular menstruation, and fatigue. If the thyroid gland produces too much T4, the rate of the patient's body functions will increase and cause symptoms associated with hyperthyroidism such as increased heart rate, anxiety, weight loss, difficulty sleeping, tremors in the hands, and puffiness around dry, irritated eyes.

What does the test include?  The HealthCheckUSA Thyroxine (T4) Thyroid Function test is a blood test that includes:

• Thyroxine (T4) Free Thyroid Function Blood Test

Who should be tested? Because the free levels of T4/T3 represent immediately available hormone, free T4 and free T3 is thought to better reflect the patient's hormonal status than total T4 and Total T3.  We recommend a thyroid test for anyone who:

• has a family member with thyroid disease
• has been diagnosed with chronic fatigue syndrome
• is a woman in or near menopause
• has recently given birth
• has other pituitary or endocrine disease
• is experiencing symptoms of thyroid disease