What are normal thyroid levels in blood?

The normal range of thyroid stimulating hormone, or TSH, in the blood is 0.4 to 5.5 mU/mL, reports Cleveland Clinic. The normal range of thyroxine, or T4, in the blood is 5 to 11 ug/dL, and the desired level of microsomal thyroid antibodies, or TPO, is 0 to 5 IU/mL.

Certain medications, including corticosteroids and aspirin, may lower the level of TSH in the blood, according to Cleveland Clinic. Heparin therapy may also lower values. Potassium, lithium and iodide may raise TSH levels. Patients may have blood drawn for a thyroid test at any time of the day, and there is no need for the patient to fast prior to being tested.