Comment on: Neutropenia and anemia with reduced serum vitamin B(12)

Abstract

To the Editor: We read with interest the case report describing a patient with a clear morphological diagnosis of acute myeloid leukemia (given the presence of Auer rods) and a total B12 level below the lower limit of detection in that laboratory. The article states, “It is quite likely that there was no tissue deficiency of B12 despite the low serum concentration. Tissue delivery of vitamin B12 depends on transcobalamin concentration whereas assays are measuring also vitamin B12 bound to haptocorrin” [1]. The measurement of a total B12 level includes both holohaptocorrin (holoHC) and holotranscobalamin, the latter also known as “active B12” as this is the physiologically active component of total B12. We recently performed a review in our laboratory of bone marrow biopsies performed on patients who also had concurrent total and active B12 levels performed. We found that of the 11 patients diagnosed with acute myeloid leukemia (AML) between 2007 and 2011 (numbers limited as clinicians generally do not order B12 levels on these patients), four patients had a low total B12 (<140 pmol/L) but only two of these four had a low active B12 level (<23 pmol/L). Supporting a diagnosis of concurrent B12 deficiency, these two patients were the most anemic and thrombocytopenic—one had hemoglobin (Hb) of 49 g/L and platelet count of 8 × 109 per L; the other had Hb 66 g/L and platelet count of 26 × 109 per L. The mean Hb of the remaining nine patients was 99 g/L with a mean platelet count of 126 × 109 per L. Of 29 patients diagnosed with myelodysplasia on a bone marrow biopsy, four had a low total B12 level but none had a low active B12 level. A low total B12 level can be seen when the active B12 level is normal; this is well recognized in pregnancy where holoHC tends to fall [2, 3]. Of a total of seven patients with bone marrows biopsies showing chronic phase chronic myeloid leukemia (CML-CP), six had an unmeasurably high total B12 level with the remaining case also showing a high total B12 of 682 pmol/L. Six of seven patients had an active B12 level within the normal range and only one was elevated. A high total B12 level can be misleading in the presence of a high holoHC. This is particularly evident in some patients with a leucocytosis [4, 5]. An active B12 level should be performed in patients with hematological disorders involving the myeloid series if there is suspicion of B12 deficiency because of the apparent variability in holoHC levels in these patients. Sarah Kamel*, Zhong Lu*, Ken Sikaris*, * Sonic Healthcare, Melbourne Pathology, Australia.