Does an elevated serum vitamin B(12) level mask actual vitamin B(12) deficiency in myeloproliferative disorders?

Elevation of the methylmalonic acid level is a sensitive marker of vitamin B(12) deficiency. Our cross-sectional observational study of 33 patients with myeloproliferative disorders found that 9 patients, 27.27% had occult deficiency despite having normal to elevated serum vitamin B(12) levels.