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Is 1.0 Low for Thyroid Function?

The thyroid is an integral part of the body and when it malfunctions, effects can be seen in the metabolism, body temperature, mood, hair, energy level, and more. Both men and women may suffer from thyroid disease, but women are at a greater risk for it. It is important to see your doctor or an endocrinologist if you feel your thyroid may be functioning too low.

  1. T4 test - Serum Thyroxine and Free Thyroxine

    • The first test a doctor will give you is the T4 test, the main thyroid hormone. There are two versions of T4--serum thyroxine and free thyroxine. The normal range for T4 serum thyroxine falls between 4.6 and 12 ug/dL. The normal range for free thyroxine falls between 0.7 and 1.9 ng/dL. A result of 1.0 would show that the serum thyroxine is too low and that the patient is at risk for hypothyroid disease. Although the result of 1.0 is within average range for the free thyroxine, a doctor may order more tests.

    T3 test - Serum Triidothyronine and FT31

    • The T3 test (also known as Free T3 Index or FT3I) is usually ordered after a patient's T4 test comes back out of average range. Average for the T3 test is 80 to 180 ng/dL, so a level of 1.0 would be considered too low.

    TSH - Serum Thyrotopin

    • Serum thyrotropin (commonly known as TSH) comes from the pituitary gland. This test measures how much T4 there is in the body. An average range is 0.5 to 6 U/ml. A level of 1.0 is within range, but a doctor may wish to order further tests since it is on the low end of the scale. The patient may be asked to come back for tests in a few months to determine whether the number is falling.

    Other tests and their averages

    • Your doctor may wish to perform other tests. Their abbreviations and ranges are:

      Free thyroxine fraction (FT4F): 0.03 to 0.005% (1.0 is too high)
      Thyroid hormone binding ratio ( HBR): 0.9 to 1.1 (1.0 is normal)
      Serum thyroglobulin (Tg): 0 to 30 ng/m (1 is within range but may be considered low)
      Radioactive iodine uptake (RAIU): 10 to 30% (1 is too low)

    Keep in mind

    • Please keep in mind that numbers may change depending on certain factors in a person's life, and the provided normal range figures may suit each person differently. Some medications, such as antibiotics or birth control, may cause a number to be higher or lower than normal. Inform your doctor of all medicines you are taking before your test. Also, consider that your doctor will plan a course of action best suited to you. Not everyone reacts the same to each medicine, so a low number may not be as much cause for alarm as long as you are feeling healthy. A good relationship with your doctor and a keen insight into your own health and happiness will go a long way with monitoring any thyroid malfunction.

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