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Patients treated for differentiated thyroid cancer take a daily thyroid hormone replacement pill called levothyroxine (also known as T4). They take it both to avoid hypothyroidism (underactive thyroid condition) and to prevent growth or recurrence of their thyroid cancer.

Usually they receive a T4 dose large enough to suppress their blood level of thyroid stimulating hormone (TSH) below the normal TSH range. This is called TSH suppression. The ATA and ETA guidelines suggest TSH suppression when a patient has active tumor or has a very aggressive tumor that has been treated with surgery and radioactive iodine (I 131).

However, about 85% of patients can be shown to be free of disease after initial tumor treatment by testing the patient' serum thyroglobulin levels and performing neck ultrasonography. When the patient is felt to be free of tumor on this basis, the ATA and ETA guidelines suggest maintaining the blood TSH in the low normal level, which is particularly important in children.

Patients whose thyroid glands have been removed will need to be on levothyroxine medication for the rest of their lives. The medication, which is necessary for maintaining a person's full health, must be taken on an empty stomach. Generally, it should not be taken with other drugs, since a large number of drugs interfere with thyroid hormone getting into the blood stream. Drugs as common as vitamins with iron can do this. It is necessary to check with the pharmacist and physician when new drugs are being prescribed

There are several brands of levothyroxine. Thyroid cancer specialist physicians recommend that patients stay on the same brand and not change unless a re-test of their blood is done 6 weeks later, because the brands may not result in the same TSH level, even at the same dose.

More information about levothyroxine is in the web site section titled "Know Your Pills."

The American Thyroid Association Guidelines (2009) have more information and recommendations. They are linked from the web site in the sections titled Newly Diagnosed and Thyroid Cancer Types.

TSH in Initial Management and Long-Term Management

The American Thyroid Association's Guidelines (2009) make several recommendations regarding TSH.

For initial TSH suppression, for high-risk and intermediate-risk patients, the guidelines recommend initial TSH below 0.1 mU/L, and, for low-risk patients TSH at or slightly below the lower limit of normal (0.1–0.5 mU/L). (Recommendation 40).

For long-term management, the guidelines recommend (Recommendation 49):

• In patients with persistent disease, the serum TSH should be maintained below 0.1mU=L indefinitely in the absence of specific contraindications.
• In patients who are clinically and biochemically free of disease but who presented with high risk disease, consideration should be given to maintaining TSH suppressive therapy to achieve serum TSH levels of 0.1–0.5mU=L for 5–10 years.
• In patients free of disease, especially those at low risk for recurrence, the serum TSH may be kept within the low normal range (0.3–2mU=L).
• In patients who have not undergone remnant ablation who are clinically free of disease and have undetectable suppressed serum Tg and normal neck ultrasound, the serum TSH may be allowed to rise to the low normal range (0.3–2mU=L).

About 85% of postoperative patients are low-risk, according to the guidelines.

The Guidelines, plus other information linked in the Newly Diagnosed section explain low, intermediate, and high risk of persistent or recurrent disease.

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