How to Read T4 Thyroid Test Numbers

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Your doctor can explain the T4 results best.

Controlled by the hypothalamus and pituitary glands, the thyroid is an endocrine gland located in the neck of the human body. This gland produces thyroid hormones triiodothyronine (T3) and thyroxine (T4). T3 and T4 regulate metabolism and other systems in the body. Thyroid tests are done to assist in the diagnosis of disease. Thyroid medication prescribed by a physician duplicates the normal human thyroid exactly.

Things You'll Need

  • Test results from your physician
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Instructions

  1. Test Results for Thyroxine (T4) Levels

    • 1

      Go to the clinic and have your blood drawn for the T4 level tests. One particular test is called radioimmunoassay (RIA). It measures thyroid function and how much T4 is in the blood. A thyroid-stimulating hormone (TSH) blood test is used to check for potential thyroid problems. The Free T4 test is one that measures the T4 not bound with proteins and can be very useful in managing hypothyroidism.

    • 2

      Study the results you receive from your doctor. If your T4 level is between 4.5 and 12.5, it is considered in the normal range. A low T4 level may mean a diseased thyroid gland or a non-functioning pituitary gland which is not stimulating the thyroid to produce T4. If the T4 level is low and TSH is not higher, the pituitary gland may be the cause of the hypothyroidism. If the T4 is low and the TSH is high, it may confirm that the thyroid gland, not the pituitary gland, is responsible for the hypothyroidism.

      If test results indicate high or low T4, or T3 which can't be explained, it may be due to an increase or decrease of protein globulin (TBG). This situation causes no problems except falsely elevating or lowering the T4 level. This causes a frequent misdiagnosis of hyperthyroidism or hypothyroidism, where there is no thyroid disorder and medication is not required. Most thyroid hormones in the blood are connected to TBG. If there is an excess or deficiency of TBG, it changes the T4 or T3 measurement.

    • 3

      Inspect your test results for abnormal readings. If abnormal results are found, this could indicate an overactive thyroid or an underactive thyroid.

      An overactive thyroid creates the condition of hyperthyroidism. Symptoms include rapid heart rate, weight loss, nervousness, a feeling of being too hot, diarrhea or irregular menstrual periods in women.

      An underactive thyroid is called hypothyroidism. Symptoms include constipation, weight gain, fatigue, dry skin, a feeling of being too cold or frequent menstrual periods in women.

Tips & Warnings

  • If you are advised by your physician that your tests are normal but you have symptoms or risk factors for thyroid disease see an alternate physician.

  • If you are prescribed thyroid medicine, it's important to follow the instructions exactly.

  • Advise your physician if you have had tests in which radioactive materials were used, or had X-rays that used iodine dye within the last six weeks. Either of these would affect the outcome of the test results.

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  • Photo Credit senior doctor 12 image by Paul Moore from Fotolia.com

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