T3, T4 & TSH are 3 most commonly asked blood tests for diagnosing and monitoring most Thyroid disorders since they are either due to increased or decreased functioning of the gland. T3 (Tri-iodo-thyronine) A T3 test determines whether the thyroid is performing properly, and is used mainly to help diagnose hyperthyroidism, since T3 becomes abnormal before T4 and returns to normal after T4. It is not usually helpful if hypothyroidism is suspected. T3 is not used as a routine thyroid test. How is interpreted? A high total or free T3 result may indicate an overactive thyroid gland (hyperthyroidism). Low total or free T3 results may indicate an underactive thyroid gland (hypothyroidism). The test results are always reported as numerical values and it is necessary to know the reference range for the particular test as it may vary by the patient's age, sex and kit used to perform the test. The reference range for the test done is printed along the test result. Any precaution? Many medications—including estrogen, certain contraceptive pills,
and large doses of aspirin—can interfere with total T3 test results. Inform your
doctor about any drugs you are taking. In general, free T3 levels are not affected by
these medications. TSH testing is used to:
When is it ordered? If a patient shows symptoms of a thyroid disorder. For example, symptoms of either hyperthyroidism or symptoms of hypothyroidism. The blood test may be ordered with other thyroid hormone tests and after a physical examination of your thyroid. How is it interpreted? A high TSH result often means an under active thyroid gland (hypothyroidism). In patients who are on Thyroid hormone medication, a high TSH value suggests that the dose has to be increased. A low TSH result can indicate an overactive thyroid gland (hyperthyroidism). In patients who are on Thyroid hormone medication, a low TSH value suggests that the dose is very high and should be stepped down. Any precautions? Many medications — including aspirin and thyroid-hormone replacement therapy — may interfere with thyroid gland function test results, so tell your doctor about any drugs you are taking. If the dose of thyroid hormone is adjusted, make sure you wait at least one to two months before you check your TSH again, allowing the new dose to have its full effect. Extreme stress and acute illness may also affect TSH test results, and results may be low during the first trimester of pregnancy. T4 A T4 test tells whether the thyroid is performing properly. Newborns are commonly screened for T4 levels as well as TSH concentrations to check for hypothyroidism, which can cause mental retardation. In adults, the T4 test generally aids in the diagnosis of hypothyroidism or hyperthyroidism. The test may also be used to help evaluate a patient with a goiter - enlarged thyroid gland. When is it ordered? In adults, a total T4 or free T4 test is usually ordered in response to an abnormal TSH test result. How is it interpreted? High free or total T4 results may indicate an overactive thyroid gland
(hyperthyroidism). Any precautions? Many medications—including estrogen, certain types of birth control pills, and large doses of aspirin—can interfere with total T4 test results, so tell your doctor about any drugs you are taking. In general, free T4 levels are not affected by these medications. Total T4 levels may be affected by contrast material used for certain X-ray imaging tests. At times your doctor may ask for antibodies (antimicrosomal or antithyroglobulin) to confirm/ rule out auto immune causes. Detailed discussion on this is outside the purview of this article. |
