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 goal for your TSH level may be 0.1 to 0.5 mU/L, which is just below or near the low end of the normal range. The goal may change to a level within the normal range, rather than below it, as time goes on.
    • In people who are medium or high risk, 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 change, depending on your body’s response to the treatment.

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Know Your Pills

  • Wherever you obtain your prescriptions, always double check your pills when you receive them to be sure that you are getting what your doctor prescribed. Do this for all of your prescriptions, not just levothyroxine.
  • Levothyroxine is the pharmaceutical name for synthetic thyroid hormone prescribed for people who have been treated for thyroid cancer. Several brand-name synthetic levothyroxine preparations are currently available. Although all of these medications are synthetic levothyroxine, they are not identical. The manufacturing processes differ, as do the fillers and dyes. These differences may affect the absorption of the drug.
  • For this reason, thyroid cancer specialist physicians recommend that thyroid cancer patients consistently take levothyroxine from the same manufacturer. If you need to change manufacturers for some reason, you should have your thyroid levels checked 6-8 weeks later, because your TSH may have changed and no longer be at the level recommended by your physician.
  • Another point to remember is that levothyroxine is temperature-sensitive, especially if above room temperature. Picking up pills at a local pharmacy helps avoid temperature extremes.
  • Store your levothyroxine pills away from heat, humidity, and light. When the weather is warm or sunny, don’t leave them in a parked car, because it can become too hot. When traveling, keep your pills from becoming exposed to heat.
  • Take your levothyroxine every day at the same time, under similar circumstances. Most people take their pill first thing in the morning. It is best to take it with a full glass of water, an hour before eating anything or drinking any other beverage. This will ensure proper absorption, because food, minerals, vitamins, and other medications can interfere with absorption.
  • After taking your levothyroxine, it is also recommended that you wait about 4 hours before taking any calcium supplements and/or vitamins containing iron. Other medications may interfere with the absorption of levothyroxine—check with your doctor or pharmacist.
  • Read the information provided by your pharmacist and tell your physician if you experience any of the symptoms noted on the bottle.
  • Following your thyroidectomy it may take one or more dosage changes to find the dosage level that is correct for you.

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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