TG and thyroid cancer: However, the precise Tg value, either basal or stimulated, that can be used to distinguish minimal residual normal tissue from persistent thyroid cancer has not been firmly established although we expect a non-stimulated thyroglobulin value obtained at least 6 weeks after surgery to be less than 5 ng/mL and often less than 2 ng/mL if a total thyroidectomy is done by an experienced thyroid surgeon (4,16).