TPO and hypothyroidism: Forty-eight percent also had serum thyroid antibodies (45% serum thyroid peroxidase antibody [TPO Ab], 31% serum thyroglobulin antibody [Tg Ab], 10% serum thyroid stimulating immunoglobulin [TSI], and 3% serum thyrotropin receptor antibody [TR Ab]) checked either at the current visit or at any time previously during the evaluation of their hypothyroidism.