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. Early detection of vitamin B(12) deficiency by using the methylmalonic acid measurement may prevent significant neurologic and hematologic complications in patients with myeloproliferative disorders. In patients with myeloproliferative disorders, normal to high serum vitamin B(12) concentrations have often been reported. The primary objective of this study was to determine whether normal or elevated serum vitamin B(12) levels in myeloproliferative disorders might actually mask the true underlying vitamin B(12) deficiency in some patients. Thirty-three patients (12 men, 21 women; mean age, 70.55 years [range, 37-90 years]) with polycythemia vera (n = 13), essential thrombocythemia (n = 12), chronic myelogenous leukemia (n = 5), and idiopathic myelofibrosis (IMF) (n = 3) were accrued over a period of 1 year, from March 2009 to February 2010. From all of the subjects, serum vitamin B(12) level, methylmalonic acid level, a basic complete blood cell count panel, and liver and renal function tests were obtained. Normal to elevated serum vitamin B(12) levels were recorded in all the patients. However, elevated serum methylmalonic acid levels were found in 9 (27.27%) patients, with a prevalence of 2 patients with polycythemia vera, 23% in polycythemia vera, 4 patients with essential thrombocythemia, 33.3% in essential thrombocythemia, 1 patient with chronic myelogenous leukemia, 20% in chronic myelogenous leukemia, and 2 patients with idiopathic myelofibrosis, 66.7% in IMF. Our data suggest that 27.27% of the total enrolled patients had occult vitamin B(12) deficiency despite normal to elevated vitamin B(12) levels on regular serum vitamin B(12) testing.