Elevated methylmalonic acid and total homocysteine levels show high prevalence of vitamin B12 deficiency after gastric surgery.
Sumner AE, Chin MM, Abrahm JL, Berry GT, Gracely EJ, Allen RH, Stabler SP. Elevated methylmalonic acid and total homocysteine levels show high prevalence of vitamin B12 deficiency after gastric surgery. Ann Intern Med. 1996 Mar 01; 124(5):469-76.