Interpreting Thyroid Lab Results
Understanding TSH Blood Levels Helps to Guide Treatment
Sep 5, 2009
Thyroid treatment is managed based on changes in thyroid blood tests. Medications for hypothyroidism and hyperthyroidism are adjusted based on thyroid levels.
Thyroid problems are very common, particularly in women and as people age. Underactive thyroid or hypothyroidism occurs when the thyroid does not produce enough thyroid hormone. Hyperthyroidism or overactive thyroid is the opposite...the thyroid produces too much thyroid hormone. Both conditions are diagnosed based on results of thyroid levels in the blood.
TSH
TSH is the test most commonly used for diagnosing and managing thyroid treatment. TSH stands for thyroid-stimulating hormone. It is sometimes called thyrotropin. TSH is a pituitary hormone that responds to levels of thyroid hormones in the blood, directing the thyroid to produce or stop producing thyroid hormone. Because of this, understanding TSH levels sometimes seems backward. TSH is low in patients with an overactive thyroid and high in someone with an underactive thyroid.
TSH in Hypothyroidism
According to the American Association of Clinical Endocrinologists (AACE), the normal range for TSH is 0.3 to 3 mIU/ml. Many labs still report results using the old range of 0.5 to 5 mIU/ml. There is still some controversy over the appropriate level for diagnosing and treating hypothyroidism. Studies show definite benefit in giving thyroid hormone replacement to people with a TSH > 10 mIU/ml. Elevated TSH from 3 to 10 mIU/ml is not so clear-cut. Some people will feel better with initiation of thyroid hormone replacement, but studies don't absolutely indicate that it's necessary.
The American Thyroid Association recommends that people on thyroid hormone replacement like levothyroxine or desiccated thyroid have their TSH levels between 0.5 and 2 mIU/ml. If the TSH is > 2 mIU/ml, the levothyroxine dose may be increased to bring the TSH lower. A TSH value < 0.5 mIU/ml may require a decrease in levothyroxine dose, particularly if the patient is feeling symptoms or has a history of heart disease.
Sometimes TSH is actually low in hypothyroidism. This occurs when the pituitary gland is not functioning properly. In this case, TSH, will be low instead of high. Other pituitary function tests must be checked to see the overall function of the pituitary.
TSH in Hyperthyroidism
Hyperthyroidism is diagnosed when the TSH is < 0.3 mIU/ml. Like hypothyroidism, patients don't always require treatment for a low level if other thyroid tests are normal. When the TSH drops to < 0.1 mIU/ml, most patients do need treatment to prevent complications of hyperthyroidism like heart arrhythmias and bone loss. People with low TSH may be treated with antithyroid medications, radioactive iodine or thyroid surgery.
During treatment with antithyroid drugs, the TSH is monitored for improvement. When the TSH becomes normal or elevated, the dose of antithyroid medication is lowered.
TSH in Thyroid Cancer
Patients who have had thyroid cancer are generally hypothyroid because they've had their thyroid removed. These patients are often given higher doses of thyroid replacement to keep their TSH levels somewhat lower, usually < 1 mIU/ml. This helps to prevent the thyroid cancer from recurring. Depending on the type of thyroid cancer and whether it invaded the lymph nodes, TSH levels may be kept as low as 0.1 to 0.3 mIU/ml.
Where a patient 'fits' into this range is somewhat subjective. Some patients feel more energy at TSH levels < 1 mIUI/ml while others feel jittery. Others may be more fatigued when the TSH drifts toward 2 mIU/ml, while others are comfortable. Thyroid patients should discuss with their healthcare provider what goal range for TSH is appropriate for them.
For information on other thyroid lab tests, check out Understanding T4 and T3 levels and What are Thyroid Antibodies?.
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