How Are TSH Levels Tested?

Doctors test the levels of thyroid stimulating hormone through a blood test, according to MedlinePlus. Though helpful, the test may result in excessive bleeding, accumulation of blood under the skin, light-headedness and infection due to skin breakage.

Thyroid stimulating hormone test is necessary when a doctor suspects hyperthyroidism or hypothyroidism, or when a doctor wants to determine the effectiveness of treatment of hypothyroidism or hyperthyroidism, notes MedlinePlus. In preparation for thyroid stimulating hormone test, a doctor may advise the patient to pause taking certain drugs that may affect the test results including potassium iodide, dopamine, amiodarone, lithium and prednisone. To perform the test, the doctor draws a blood sample from the patient's vein using a needle and takes the sample to a lab for analysis. The patient may feel slight pain or a prick during the insertion of the needle, followed by temporary throbbing.

Normal range for blood thyroid stimulating hormone is 0.4 to 4.0 milli-international units per liter, says MedlinePlus. However, there may be a variation of the normal range from one lab to another because of the difference in measurements and samples tested. Results that are below the normal range may imply that the patient has hyperthyroidism, which is an overactive thyroid gland. If the level of thyroid stimulating hormone is higher than the normal range, the implication is that the patient has hypothyroidism, which is an underactive thyroid gland.