Vitamin B12 Abstracts 3

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The pathophysiology of elevated vitamin B12 in clinical practice.
            (Andrès et al., 2013) Download
Hypercobalaminemia (high serum vitamin B12 levels) is a frequent and underestimated anomaly. Clinically, it can be paradoxically accompanied by signs of deficiency, reflecting a functional deficiency linked to qualitative abnormalities, which are related to defects in tissue uptake and action of vitamin B12. The aetiological profile of high serum cobalamin predominantly encompasses severe disease entities for which early diagnosis is critical for prognosis. These entities are essentially comprised of solid neoplasms, haematological malignancies and liver and kidney diseases. This review reflects the potential importance of the vitamin B12 assay as an early diagnostic marker of these diseases. A codified approach is needed to determine the potential indications of a search for high serum cobalamin and the practical clinical strategy to adopt upon discovery of elevated cobalamin levels. While low serum cobalamin levels do not necessarily imply deficiency, an abnormally high serum cobalamin level forms a warning sign requiring exclusion of a number of serious underlying pathologies. Functional cobalamin deficiency can thus occur at any serum level.

Elevated plasma vitamin B12 levels as a marker for cancer: a population-based cohort study.
            (Arendt et al., 2013) Download
BACKGROUND:  A substantial proportion of patients referred for plasma vitamin B12 (cobalamin [Cbl]) measurement present with high Cbl levels, which have been reported in patients with different cancer types. However, the cancer risk among patients with newly diagnosed high Cbl levels has not been adequately examined. METHODS:  We conducted this cohort study using population-based Danish medical registries. Patients referred for Cbl measurement with levels greater than the lower reference limit (≥200 pmol/L) were identified from the population of Northern Denmark during the period of 1998 to 2009 using a database of laboratory test results covering the entire population. Data on cancer incidence (follow-up 1998-2010), Cbl treatment, and prior diagnoses were obtained from medical registries. Patients receiving Cbl treatment were excluded. Cancer risks were calculated as standardized incidence ratios (SIRs) with 95% confidence intervals (CIs), stratified by plasma Cbl levels. All statistical tests were two-sided. RESULTS:  We identified 333 667 persons without prevalent cancer and not receiving Cbl treatment. Six percent had Cbl levels greater than the upper reference limit (≥601 pmol/L). Cancer risk increased with higher Cbl levels and was highest during the first year of follow-up (Cbl 601-800 pmol/L: SIR = 3.44, 95% CI = 3.14 to 3.76; Cbl >800 pmol/L: SIR = 6.27, 95% CI = 5.70 to 6.88; both P < .001). The risks were particularly elevated for hematological and smoking- and alcohol-related cancers for persons with high Cbl levels. CONCLUSIONS:  High Cbl levels were associated with the risk of subsequently diagnosed cancer, mostly within the first year of follow-up. This may have clinical implications for the interpretation of high Cbl levels.

Unexpected high plasma cobalamin : proposal for a diagnostic strategy.
            (Arendt and Nexo, 2013) Download
It is well-established that more than 8% of patients examined for vitamin B12 deficiency unexpectedly have increased plasma levels of the vitamin, but so far there are no guidelines for the clinical interpretation of such findings. In this review, we summarise known associations between high plasma cobalamin and diseases. We report associations mainly with cancer, liver and kidney diseases, but also with a number of other diagnostic entities. The pathogenic background is poorly understood and is likely to be multi-factorial, involving increased concentrations of one or both of the circulating cobalamin binding proteins, transcobalamin and haptocorrin. Based on current knowledge, we suggest a strategy for the clinical interpretation of unexpected high plasma cobalamin. Since a number of the associated diseases are critical and life-threatening, the strategy promotes the concept of 'think the worst first'. It is important to realise that high cobalamin levels can be an unspecific marker for cancer. If this can be ruled out, diseases of the liver and kidney should be considered.

Circulating antibody to transcobalamin II causing retention of vitamin B12 in the blood.
            (Carmel et al., 1977) Download
A patient with recurrent pulmonary abscess, weight loss, and alcoholism was found to have extremely high serum vitamin B12 and unsaturated vitamin B12-binding capacity (UBBC) levels. While transcobalamin (TC) II was also increased, most of his UBBC was due to an abnormal binding protein which carried greater than 80% of the endogenous vitamin B12 and was not found in his saliva, granulocytes, or urine. This protein was shown to be a complex of TC II and a circulating immunoglobulin (IgGkappa and IgGlambda). Each IgG molecule appeared to bind two TC II molecules. The reacting site did not interfere with the ability of TC II to bind vitamin B12, but did interfere with its ability to transfer the vitamin to cells in vitro. The site was not identical to that reacting with anti-human TC II antibody produced in rabbits. Because of this abnormal complex, 57Co-vitamin B12 injected intravenously was cleared slowly by the patient. However, no metabolic evidence for vitamin B12 deficiency was demonstrable, although the patient initially had megaloblastic anemia apparently due to folate deficiency. The course of the vitamin B12-binding abnormalities was followed over 4 yr and appeared to fluctuate with the status of the patient's illness. The IgG-TC II complex resembled one induced in some patients with pernicious anemia by intensive treatment with long-acting vitamin B12 preparations. The mechanism of induction of the antibody formation in our patient is unknown.

Intrinsic factor blocking antibody interference is not detected in five automated cobalamin immunoassays.
            (Merrigan et al., 2014) Download
OBJECTIVES:  To systematically assess five automated cobalamin assays for intrinsic factor binding antibody (IFBA)-induced interference using pooled serum. METHODS:  Six pools created from IFBA-negative and IFBA-positive serum representing low, normal, and high cobalamin concentrations were analyzed before and after polyethylene glycol (PEG) precipitation of immunoglobulins on five cobalamin assays: the Centaur XP (Siemens Healthcare Diagnostics, Tarrytown, NY), IMMULITE 2000 (Siemens Healthcare Diagnostics), ARCHITECT i2000SR (Abbott Diagnostics, Abbott Park, IL), UniCel Dxl 800 (Beckman Coulter, Chaska, MN), and Modular E170 (Roche Diagnostics, Indianapolis, IN). RESULTS:  Cobalamin concentrations before and after PEG treatment were similar, almost all within a 30% total allowable error, with no difference in pattern between the IFBA-negative and IFBA-positive pools regardless of the cobalamin concentration. CONCLUSIONS:  Our results suggest that, under optimal conditions, the five automated cobalamin assays assessed are not susceptible to IFBA-mediated interference.

Immune complexes and persistent high levels of serum vitamin B12.
            (Remacha et al., 2013) Download
INTRODUCTION: Patients with persistent high levels of serum vitamin B12 were often referred to Hematology departments. In this study, characteristic of patients with serum vitamin B12 levels higher than 2500 pmol/L (high B12) were studied. METHODS: Prevalence of high B12 was evaluated during a 10-month period. Samples with high B12 were incubated with polyethylene glycol (PEG) and a new measurement of vitamin B12 was carried out using the supernatant. As a pilot study, 26 frozen samples with high B12 were evaluated for changes in vitamin B12 after PEG. Moreover, a prospective study was carried out during three consecutive months. Size exclusion chromatography was employed to demonstrate the presence of immune complexes (ICs) with plasma vitamin B12-binding proteins in some serum samples with high B12. RESULTS: Prevalence of high B12 was 1.3%. Results from 26 frozen samples and from a prospective study (28 cases) showed that undergoing vitamin B12 treatment was the main cause of high B12. However, ICs were detected in 10 frozen samples and in seven cases (25%) of the prospective study, respectively. Serum vitamin B12 decreased to normal values after precipitation with PEG, and size exclusion chromatography confirmed ICs. An association with autoimmune or hematological disorders was observed. CONCLUSIONS: In patients with repeatedly high B12 levels, ICs were detected in approximately 25% of samples. Precipitation with PEG is an easy method to confirm the presence of ICs and to evaluate serum vitamin B12 levels in these patients.

The methyl folate trap. A physiological response in man to prevent methyl group deficiency in kwashiorkor (methionine deficiency) and an explanation for folic-acid induced exacerbation of subacute combined degeneration in pernicious anaemia.
            (Scott and Weir, 1981) Download
It is suggested that in man the methyl folate trap is a normal physiological response to impending methyl group deficiency resulting from a very low supply of methionine. This decreases cellular S-adenosyl-methionine (SAM), which puts at risk important methylation reactions, including those required to maintain myelin. In order to protect these methylation reactions, the cell has evolved two mechanisms to maintain supplies of methionine and SAM as a first priority. (a) Decreased SAM causes the folate co-factors to be directed through the cycle involving 5-methyl-tetrahydrofolate (5-methyl-THF) and methionine synthetase and away from the cycles that produce purines and pyrimidines for DNA synthesis. This enhances the remethylation of homocysteine to methionine and SAM. In addition, by restricting DNA biosynthesis and with it cell, division, competition for methionine for protein synthesis is reduced. Thus, whatever methionine is available is conserved for the vital methylation reactions in the nerves, brain, and elsewhere. (b) 5-methyl-THF, the form in which almost all folate is transported in human plasma, must react with intracellular homocysteine before it can be retained by the cell as a polyglutamate. Since homocysteine is derived entirely from methionine, methionine deficiency will cause intracellular folate deficiency, and the rate of mitosis of rapidly dividing cells will be reduced. although these two processes have evolved as a response to methionine deficiency, they also occur in B12 deficiency, which the cell mistakenly interprets as lack of methionine. the resulting response is inappropriate and gives rise to a potentially lethal anaemia. In these circumstances the methylation reactions are also partly protected by the reduced rate of cell division. This explains why administration of folic acid, which induces cell division and use of methionine in protein synthesis, impairs methylation of myelin and precipitates or exacerbates subacute combined degeneration (SCD). During folate deficiency methionine biosynthesis is also diminished. As in methionine deficiency, the body responds to decreasing availability of SAM by diverting folate away from DNA biosynthesis towards the remethylation of homocysteine to methionine and SAM. The selective use pf available folate to conserve methionine, together with the ability of nerve tissue to concentrate folate form the plasma, explains the absence of SCD in folate deficiency.

Falsely elevated cobalamin concentration in multiple assays in a patient with pernicious anemia: a case study.
            (van Rossum et al., 2013) Download


 

References

Andrès, E, et al. (2013), ‘The pathophysiology of elevated vitamin B12 in clinical practice.’, QJM, 106 (6), 505-15. PubMedID: 23447660
Arendt, JF, et al. (2013), ‘Elevated plasma vitamin B12 levels as a marker for cancer: a population-based cohort study.’, J Natl Cancer Inst, 105 (23), 1799-805. PubMedID: 24249744
Arendt, JF and E Nexo (2013), ‘Unexpected high plasma cobalamin : proposal for a diagnostic strategy.’, Clin Chem Lab Med, 51 (3), 489-96. PubMedID: 23241600
Carmel, R, B Tatsis, and L Baril (1977), ‘Circulating antibody to transcobalamin II causing retention of vitamin B12 in the blood.’, Blood, 49 (6), 987-1000. PubMedID: 861380
Merrigan, SD, DT Yang, and JA Straseski (2014), ‘Intrinsic factor blocking antibody interference is not detected in five automated cobalamin immunoassays.’, Am J Clin Pathol, 141 (5), 702-5. PubMedID: 24713742
Remacha, AF, et al. (2013), ‘Immune complexes and persistent high levels of serum vitamin B12.’, Int J Lab Hematol, PubMedID: 23998297
Scott, JM and DG Weir (1981), ‘The methyl folate trap. A physiological response in man to prevent methyl group deficiency in kwashiorkor (methionine deficiency) and an explanation for folic-acid induced exacerbation of subacute combined degeneration in pernicious anaemia.’, Lancet, 2 (8242), 337-40. PubMedID: 6115113
van Rossum, AP, LT Vlasveld, and A Castel (2013), ‘Falsely elevated cobalamin concentration in multiple assays in a patient with pernicious anemia: a case study.’, Clin Chem Lab Med, 51 (9), e217-9. PubMedID: 23729575