Low T3 levels can be observed in hypothyroidism, but more often this test is useful in the diagnosis and management of hyperthyroidism, where T3 levels are elevated. Normal range: 100 - 200 ng/dL (nanograms per deciliter of blood).

Why is T3 normal in hypothyroidism?

Primary hypothyroidism is virtually the only disease that is characterized by sustained rises in TSH levels. As the TSH level increases early in the disease, conversion of T4 to T3 increases, maintaining T3 levels. In early hypothyroidism, TSH levels are elevated, T4 levels are normal to low, and T3 levels are normal.

What is T3 levels thyroid?

This test measures the level of triiodothyronine (T3) in your blood. T3 is one of two major hormones made by your thyroid, a small, butterfly-shaped gland located near the throat. The other hormone is called thyroxine (T4.) T3 and T4 work together to regulate how your body uses energy.