Thyroid Hormone Replacement, TSH, Thyroglobulin, and Other Blood Testing

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Thyroid Hormone Replacement Therapy
Know Your Pills
Understanding Your Blood Tests
If You Have Hypoparathyroidism
For More Information

Thyroid Hormone Replacement Therapy

If your thyroid was removed surgically, you will receive thyroid hormone replacement therapy (levothyroxine) for the rest of your life.

  • If you have papillary, follicular, or one of their variants, your dose of thyroid hormone replacement will be set for a target TSH level tailored to your individual risk of persistent or recurrent disease. Your doctor will order blood tests periodically to ensure that you are on the proper dose of thyroid hormone replacement.
    • In low-risk patients, the 2015 American Thyroid Association Guidelines recommend that the goal for your initial TSH level usually be 0.5 to 2.0 mU/L, which is within the normal range. For some patients, the goal is 0.1 to 0.5 mU/L, which is just below or near the low end of the normal range. This lower TSH goal may change over time to 0.5 to 2.0 mU/L, based on your response to treatment.
    • In intermediate-risk patients, the initial TSH goal is 0.1 to 0.5 mU/L. This goal may change to a level within the normal range if you have an excellent response to treatment.

    • For high-risk patients, the dose will be high enough to suppress the thyroid stimulating hormone (TSH) below the range that is normal for someone not diagnosed with thyroid cancer. The goal is to prevent the growth of cancer cells while providing essential thyroid hormone to the body. At first, your TSH will probably be suppressed to below 0.1 mU/L. The level may later change to 0.1 to 0.5, depending on your body’s response to the treatment.

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Understanding Your Blood Tests

During the first year after your treatment, your physician may order blood tests several times to make sure you are on the right dosage of thyroid hormone replacement.

Blood testing also helps monitor for persistent or recurrent cancer.

After the first year, your doctor may order blood tests less often.

Among events that may affect your dosage of thyroid hormone replacement are weight gain or loss, pregnancy, and menopause. However, you will generally be on the same dosage for long periods of time.

Papillary and Follicular Thyroid Cancer and their Variants

There are three main blood tests:

  • Thyroid Stimulating Hormone (TSH). See the section above on thyroid hormone replacement therapy.
  • Thyroglobulin (Tg): Thyroglobulin is a protein produced by thyroid cells (both normal and cancerous cells). After removal of the thyroid gland, Thyroglobulin can be used as a "cancer marker." Its number should be as low as possible. Sometimes this is termed "undetectable.” After your surgery and RAI, it may take months or years for the Tg number to come down to zero or undetectable.

    A positive Tg test indicates that thyroid cells, either normal or cancerous, are still present in your body. Depending on the level of Tg in your blood, your doctor may want to monitor you more closely with other tests or scans and/or prescribe additional treatment.

    If you did not receive RAI, your Tg level will probably be detectable. This is because some remnant thyroid tissue nearly always remains in your neck after surgery. If you had a lobectomy rather than a thyroidectomy, your remaining lobe will almost certainly produce Tg. However, it is still helpful to follow your Tg levels over time. If Tg levels increase, your doctor may recommend further imaging studies to locate the source.

    From time to time, your doctor may recommend what is called a “stimulated Tg” measurement. This means that your TSH is elevated, by withdrawal from thyroid hormone or by receiving injections of the drug Thyrogen®, and then your Tg is measured. Thyroglobulin testing can be more accurate when your TSH level is elevated.
  • Anti-thyroglobulin antibodies (TgAb): Some people produce anti-thyrogloblin antibodies. These are not harmful. However, they mask the reliability of the Tg value. If you have TgAb, imaging studies may be used to monitor for persistent or recurrent disease. Sometimes the antibodies disappear over time, although not always.

In addition to these tests described above, some doctors will also recommend the measurement of Free T4. If so, discuss this with your doctor.

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If You Have Hypoparathyroidism

If you experienced parathyroid loss or damage during your thyroid surgery, maintaining proper calcium levels will be an ongoing concern. You will have your blood calcium levels monitored, and will receive further instructions.

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Last updated: May 21, 2013