Unfortunately, current assays for measuring Tg in blood samples are not sensitive enough to reliably measure Tg while patients are under thyroid hormone replacement therapy. Instead patients have to withdraw thyroid hormone for several weeks or receive costly injections of recombinant thyroid stimulating hormone (TSH) in order to raise Tg production by thyroid remnant and/or thyroid cancer cells so that it can be measured by current Tg assays. Other patients have antibodies against Tg that interfere in current immunoassays.