Does an Elevated Serum Vitamin B12 Level Mask Actual Vitamin B12 Deficiency in Myeloproliferative Disorders?

In patients with myeloproliferative disorders, normal to high serum vitamin B12 concentrations have often been reported. The primary objective of this study was to determine whether normal or elevated serum vitamin B12 levels in myeloproliferative disorders might actually mask the true underlying vitamin B12 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 B12 level, methylmalonic acid level, a basic complete blood cell count panel, and liver and renal function tests were obtained. Normal to elevated serum vitamin B12 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 B12 deficiency despite normal to elevated vitamin B12 levels on regular serum vitamin B12 testing.