Does an Elevated Serum Vitamin B12 Level Mask Actual Vitamin B12 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 nnethylmalonic 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.