In a patient with a normal free T4, what TSH level defines hypothyroidism?

In a patient with a normal free T4, what TSH level defines hypothyroidism?

• A. < 1 U/mL
• B. < 5 U/mL
• C. > 2.5 U/mL
• D. > 10 U/mL

Answer: (D)

TSH is the most sensitive indicator of thyroid function. If free T4 is normal, an elevated TSH means subclinical hypothyroidism, but there’s a threshold that guides treatment decisions. A TSH above 10 mIU/L is the level at which clinicians commonly define hypothyroidism that warrants treatment, even with a normal free T4, because the risk of progression to overt hypothyroidism and potential cardiovascular effects increases. Mild elevations between the upper limit of normal and 10 mIU/L are often managed with observation and individualized consideration of symptoms, antibodies, pregnancy, and other risk factors.

TSH is the most sensitive indicator of thyroid function. If free T4 is normal, an elevated TSH means subclinical hypothyroidism, but there’s a threshold that guides treatment decisions. A TSH above 10 mIU/L is the level at which clinicians commonly define hypothyroidism that warrants treatment, even with a normal free T4, because the risk of progression to overt hypothyroidism and potential cardiovascular effects increases. Mild elevations between the upper limit of normal and 10 mIU/L are often managed with observation and individualized consideration of symptoms, antibodies, pregnancy, and other risk factors.