If you’re making too much thyroid hormone, your TSH will go down.”. What’s normal can vary, depending on a number of factors, including the laboratory where your blood test is done, she adds. A normal range for TSH in most laboratories is 0.4 milliunits per liter (mU/L) to 4.0 mU/L. If your TSH is higher than 4.0 mU/L on repeat tests, you probably have hypothyroidism. Your doctor may also order a T4 test. Most of the T4 in your blood attaches to a protein, and when it does, it can’t get into your cells.