The TSH blood test measures thyroid stimulating hormone levels and is used to diagnose and monitor thyroid problems. Abnormal levels can indicate hypothyroidism or hyperthyroidism, and medication doses may need adjusting. Other thyroid blood tests can provide more accurate results, and certain factors can affect the test’s accuracy.
A TSH blood test measures thyroid stimulating hormone (TSH) in the body. The test evaluates the possibility of a thyroid problem in the patient. It is performed through a simple blood sample, and is used both for an initial diagnosis and for continuous monitoring of thyroid function. The TSH blood test is usually done in a lab or doctor’s office and takes only a few minutes.
TSH blood test is often ordered by a doctor when signs of hypothyroidism or hyperthyroidism are present. It can also help pinpoint the specific cause of hypothyroidism. Thyroid blood testing is also ordered periodically for patients who are taking medications for both thyroid conditions, to determine if current medication doses are correct. Newborns sometimes have a TSH blood test to check for low thyroid function.
Abnormal levels of thyroid stimulating hormone could indicate a thyroid problem. Elevated TSH levels typically indicate hypothyroidism, which means that the thyroid gland is underactive. Low TSH levels could mean that your thyroid is overactive, a condition called hyperthyroidism. If the TSH blood test comes back indicating high or low TSH levels, further thyroid blood tests may be requested.
High or low TSH levels in patients already diagnosed with a thyroid condition can indicate improper medication levels. Low levels in a patient with hypothyroidism could mean the dose is too high, while high TSH levels could mean the drug dose is too low. The test results help a doctor adjust the medication dosage to keep TSH levels in the normal range.
Tests for T3, T4, and thyroid antibodies are other possibilities. Thyroid stimulating hormone regulates the production of T3, or triiodothyronine, and T4, or thyroxine. T3 and T4 tests can give a more accurate picture of the patient’s thyroid problems. Low T3 and T4 levels usually accompany high TSH levels in those with hypothyroidism. Elevated T3 and T4 levels are associated with low TSH levels in patients with hyperthyroidism.
Some factors affect the accuracy of a TSH blood test, including stress or chronic illness. Certain medications can also affect results, including dopamine, lithium, heparin, levodopa, corticosteroids, methimazole, and propylthiouracil. X-rays or tests using radioactive materials in the last four to six weeks also sometimes cause inaccurate results. Thyroid-stimulating hormone levels might also be low during the first trimester of pregnancy. Your doctor should know about any of these factors before doing the TSH blood test.
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