T4,Thyroxine

This is a test used to help check thyroid gland function. It is a test which may be ordered in response to an abnormal TSH test result or when a patient has symptoms of hyper- or hypothyroidism. This test is commonly performed on newborns.

This 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 thyroid is a small, butterfly-shaped gland located just below the Adam's apple. This gland plays a vital role in controlling the rate at which your body uses energy.

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.

SAMPLE COLLECTION

A blood sample is obtained from a needle placed in a vein in your arm or from pricking the heel of an infant.

NORMAL FINDINGS

  • 1-3 days: 11-22 mcg/dL

  • 1-2 weeks: 10-16 mcg/dL

  • 1-4 months: 8-16 mcg/dL

  • 1-5 years: 7-15 mcg/dL

  • 5-10 years: 6-13 mcg/dL

  • 10-15 years: 5-12 mcg/dL

  • Adult male: 4-12 mcg/dL or 51-154 nmol/L (SI units)

  • Adult female: 5-12 mcg/dL or 64-154 nmol/L (SI units)

  • Adult over 60 years: 5-11 mcg/dL or 64-142 nmol/L (SI units)

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.