More than 10 million Americans have been diagnosed with thyroid disease, and another 13 million people are estimated to have undiagnosed thyroid problems in the U.S. alone. Women are at greatest risk, developing thyroid problems seven times more often than men. Thyroid hormones are transported in the blood "bound" to Thyroid Binding Globulin (TBG), which temporarily holds them inactive. This protein may be manipulated by many illnesses and medications. Therefore, measurement of the "unbound," free levels of T3 and T4 thyroid hormones provides a more accurate interpretation. When TSH, free T3 and T4 are found to be within normal range, a functional thyroid deficiency may be suspected. This can be clarified by testing TPO antibodies (Thyroid Peroxidase Antibody) as part of ZRT's bloodspot thyroid panel.