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What Is Third Generation TSH?

By Candi Lemon ; Updated July 27, 2017

Thyroid-stimulating hormone (TSH) is produced by the pituitary gland (at the base of the brain) to regulate the amounts of thyroid hormones in blood and help control the rate at which the body uses energy. Third generation TSH refers to the laboratory test that measures the amount of TSH in blood even at very low concentrations.


Third generation TSH differs from first and second generations in that it has a functional sensitivity (the lowest TSH concentration the test can measure accurately) of 0.01 to 0.02, which is lower than other generation TSH tests.


Doctors use third generation TSH testing to screen for thyroid disorders and monitor TSH levels in those using thyroid medications. Doctors may also use the test to diagnose and monitor infertility problems in females.


A low third generation TSH levels indicates an overactive thyroid gland (hyperthyroidism), where a high third generation TSH reflects an underactive thyroid gland (hypothyroidism). Both conditions express themselves in symptoms like fatigue/nervousness and weight loss/gain. After using third generation TSH to diagnose them, doctors can prescribe medications that keep thyroid hormones under control and get rid of the symptoms.


Certain drugs may interfere with third generation TSH testing. Patients should inform their doctor of any medication they are taking before collection of the blood sample when a trained practitioner draws a blood sample from a vein in the patient's arm.


Doctors may require additional testing to achieve a final diagnosis for a thyroid condition. Typically, third generation TSH test is accompanied by thyroxine (T4) and triiodothyronine (T3) to obtain a larger picture of thyroid health.

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