TPO and vitamin B12 deficiency: As the availability of data about the association between vitamin B12 deficiency and SCH was limited all over the world and particularly in our locality, the present study was aimed at evaluating the serum levels of both vitamin B12 and its transporter protein HoloTC in SCH patients compared with apparently healthy control subjects and to ascertain the association of mean vitamin B12 and HoloTC with the risky levels of TSH and the positivity of the anti-thyroid peroxidase (anti-TPO) antibodies.