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Devi S, Pasanna RM, Shamshuddin Z, Bhat K, Sivadas A, Mandal AK, Kurpad AV. Measuring vitamin B-12 bioavailability with [13C]-cyanocobalamin in humans. Am J Clin Nutr 2020; 112:1504-1515. [PMID: 32844171 DOI: 10.1093/ajcn/nqaa221] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Accepted: 07/10/2020] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND Vitamin B-12 deficiency is widespread in many parts of the world, affecting all age groups and increasing with age. It is primarily due to a low intake of animal source foods or malabsorption. The measurement of bioavailability of vitamin B-12 is etiologically important in deficiency but is limited due to the use of radioactive isotopes like [57Co]- or [14C]-cyanocobalamin. OBJECTIVES The aim of this study was to measure the bioavailability of [13C]-cyanocobalamin in humans and to assess the effect of parenteral replenishment of vitamin B-12 on the bioavailability. METHODS We synthesized a stable isotope-labeled vitamin B-12, [13C]-cyanocobalamin, using Salmonella enterica by providing [13C2]-ethanolamine as a sole carbon source. After purification and mass spectrometry-based characterization, its oral bioavailability was measured in the fasted state with high and low oral doses, before and after parenteral replenishment of vitamin B-12 stores, from the kinetics of its plasma appearance in a 2-compartment model. RESULTS [13C]-cyanocobalamin was completely decyanated to [13C]-methylcobalamin describing metabolic utilization, and its plasma appearance showed early and late absorption phases. At a low dose of 2.3 µg, the mean bioavailability was 46.2 ± 12.8 (%, mean ± SD, n = 11). At a higher dose of 18.3 µg, the mean bioavailability was 7.6 ± 1.7 (%, mean ± SD, n = 4). Parenteral replenishment of the vitamin B-12 store in deficient individuals prior to the measurement resulted in a 1.9-fold increase in bioavailability. CONCLUSIONS Vitamin B-12 bioavailability is dose dependent and at a low dose that approximates the normal daily requirement (46%). The stable isotope method described here could be used to define the etiology of deficiency and to inform the dietary requirement in different physiologic states as well as the dose required for supplementation and food fortification. This trial was registered at the Clinical Trials Registry of India as CTRI/2018/04/012957.
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Affiliation(s)
- Sarita Devi
- Division of Nutrition, St. John's Research Institute, St. John's National Academy of Health Sciences, Bangalore, India
| | - Roshni M Pasanna
- Division of Nutrition, St. John's Research Institute, St. John's National Academy of Health Sciences, Bangalore, India
| | - Zeeshan Shamshuddin
- Division of Nutrition, St. John's Research Institute, St. John's National Academy of Health Sciences, Bangalore, India
| | - Kishor Bhat
- Division of Nutrition, St. John's Research Institute, St. John's National Academy of Health Sciences, Bangalore, India
| | - Ambily Sivadas
- Division of Nutrition, St. John's Research Institute, St. John's National Academy of Health Sciences, Bangalore, India
| | - Amit K Mandal
- Division of Clinical Proteomics, St. John's Research Institute, St. John's National Academy of Health Sciences, Bangalore, India
| | - Anura V Kurpad
- Department of Physiology, St. John's Medical College, St. John's National Academy of Health Sciences, Bangalore, India
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Diagnostic Accuracy of Holotranscobalamin, Vitamin B12, Methylmalonic Acid, and Homocysteine in Detecting B12 Deficiency in a Large, Mixed Patient Population. DISEASE MARKERS 2020; 2020:7468506. [PMID: 32089757 PMCID: PMC7017578 DOI: 10.1155/2020/7468506] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Revised: 11/26/2019] [Accepted: 12/23/2019] [Indexed: 11/17/2022]
Abstract
Four biomarkers are commonly employed to diagnose B12 deficiency: vitamin B12 (B12), holotranscobalamin (HoloTC), methylmalonic acid (MMA), and homocysteine (Hcy). 4cB12, a combined index of the B12 status, has been suggested to improve the recognition of B12 deficiency. We aimed to evaluate the four different markers for detecting B12 deficiency, as determined by 4cB12. Within a large, mixed patient population, 11,833 samples had concurrent measurements of B12, HoloTC, MMA, and Hcy. 4cB12 was calculated according to the methods described by Fedosov. Diagnostic cutoffs as well as diagnostic accuracy for the detection of B12 deficiency were assessed with receiver operating characteristic (ROC) analysis. The median age was 56 years, and women accounted for 58.8% of the samples. Overall, the area under the curve (AUC) for the detection of subclinical B12 deficiency was highest for HoloTC (0.92), followed by MMA (0.91), B12 (0.9) and Hcy (0.78). The difference between HoloTC and B12 was driven by a significantly higher AUC for HoloTC (0.93) than for B12 (0.89), MMA (0.91), and Hcy in women 50 years and older (0.79; p < 0.05 for all). In the detection of subclinical B12 deficiency, there were no significant differences in the AUCs of HoloTC, B12, and MMA among men and women <50 years. In conclusion, in women < 50 years and in men, HoloTC, MMA, or Hcy do not appear superior to B12 for the detection of B12 deficiency. For women 50 years and older, HoloTC seems to be the preferred first-line marker for the detection of subclinical B12 deficiency.
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Brito A, Habeych E, Silva-Zolezzi I, Galaffu N, Allen LH. Methods to assess vitamin B12 bioavailability and technologies to enhance its absorption. Nutr Rev 2019; 76:778-792. [PMID: 29931214 DOI: 10.1093/nutrit/nuy026] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Vitamin B12 (B-12) deficiency is still relatively common in low-, medium-, and high-income countries, mainly because of dietary inadequacy and, to a lesser extent, malabsorption. This narrative review is based on a systematic search of evidence on methods to assess B-12 bioavailability and technologies to enhance its absorption. A total of 2523 scientific articles identified in PubMed and 1572 patents identified in Orbit Intelligence were prescreened. Among the reviewed methods, Schilling's test and/or its food-based version (using cobalamin-labeled egg yolk) were used for decades but have been discontinued, largely because they required radioactive cobalt. The qualitative CobaSorb test, based on changes in circulating holo-transcobalamin before and after B-12 administration, and the 14C-labeled B-12 test for quantitative measurement of absorption of a low-dose radioactive tracer are currently the best available methods. Various forms of B-12 co-formulated with chemical enhancers (ie, salcaprozate sodium, 8-amino caprylate) or supplied via biotechnological methods (ie, microbiological techniques, plant cells expressing cobalamin binding proteins), encapsulation techniques (ie, emulsions, use of chitosan particles), and alternative routes of administration (ie, intranasal, transdermal administration) were identified as potential technologies to enhance B-12 absorption in humans. However, in most cases the evidence of absorption enhancement is limited.
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Affiliation(s)
- Alex Brito
- I.M. Sechenov First Moscow State Medical University, Moscow, Russia
| | | | | | | | - Lindsay H Allen
- United States Department of Agriculture, Agricultural Research Service, Western Human Nutrition Research Center, Davis, California, USA
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Garrod MG, Rossow HA, Calvert CC, Miller JW, Green R, Buchholz BA, Allen LH. 14C-Cobalamin Absorption from Endogenously Labeled Chicken Eggs Assessed in Humans Using Accelerator Mass Spectrometry. Nutrients 2019; 11:nu11092148. [PMID: 31500393 PMCID: PMC6769442 DOI: 10.3390/nu11092148] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2019] [Revised: 08/31/2019] [Accepted: 09/04/2019] [Indexed: 12/27/2022] Open
Abstract
Traditionally, the bioavailability of vitamin B-12 (B12) from in vivo labeled foods was determined by labeling the vitamin with radiocobalt (57Co, 58Co or 60Co). This required use of penetrating radioactivity and sometimes used higher doses of B12 than the physiological limit of B12 absorption. The aim of this study was to determine the bioavailability and absorbed B12 from chicken eggs endogenously labeled with 14C-B12 using accelerator mass spectrometry (AMS). 14C-B12 was injected intramuscularly into hens to produce eggs enriched in vivo with the 14C labeled vitamin. The eggs, which provided 1.4 to 2.6 μg of B12 (~1.1 kBq) per serving, were scrambled, cooked and fed to 10 human volunteers. Baseline and post-ingestion blood, urine and stool samples were collected over a one-week period and assessed for 14C-B12 content using AMS. Bioavailability ranged from 13.2 to 57.7% (mean 30.2 ± 16.4%). Difference among subjects was explained by dose of B12, with percent bioavailability from 2.6 μg only half that from 1.4 μg. The total amount of B12 absorbed was limited to 0.5–0.8 μg (mean 0.55 ± 0.19 μg B12) and was relatively unaffected by the amount consumed. The use of 14C-B12 offers the only currently available method for quantifying B12 absorption in humans, including food cobalamin absorption. An egg is confirmed as a good source of B12, supplying approximately 20% of the average adult daily requirement (RDA for adults = 2.4 μg/day).
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Affiliation(s)
- Marjorie G Garrod
- USDA, ARS Western Human Nutrition Research Center, Davis, CA 95616, USA.
| | - Heidi A Rossow
- Population Health and Reproduction, University of California, Davis, CA 95616, USA.
| | | | - Joshua W Miller
- Department of Nutritional Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
| | - Ralph Green
- Department. of Medical Pathology and Laboratory Medicine, University of California, Davis, Sacramento, CA 95817, USA.
| | - Bruce A Buchholz
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
| | - Lindsay H Allen
- USDA, ARS Western Human Nutrition Research Center, Davis, CA 95616, USA.
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Allen LH, Miller JW, de Groot L, Rosenberg IH, Smith AD, Refsum H, Raiten DJ. Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review. J Nutr 2018; 148:1995S-2027S. [PMID: 30500928 PMCID: PMC6297555 DOI: 10.1093/jn/nxy201] [Citation(s) in RCA: 139] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 07/06/2017] [Accepted: 08/02/2018] [Indexed: 12/31/2022] Open
Abstract
This report on vitamin B-12 (B12) is part of the Biomarkers of Nutrition for Development (BOND) Project, which provides state-of-the art information and advice on the selection, use, and interpretation of biomarkers of nutrient exposure, status, and function. As with the other 5 reports in this series, which focused on iodine, folate, zinc, iron, and vitamin A, this B12 report was developed with the assistance of an expert panel (BOND B12 EP) and other experts who provided information during a consultation. The experts reviewed the existing literature in depth in order to consolidate existing relevant information on the biology of B12, including known and possible effects of insufficiency, and available and potential biomarkers of status. Unlike the situation for the other 5 nutrients reviewed during the BOND project, there has been relatively little previous attention paid to B12 status and its biomarkers, so this report is a landmark in terms of the consolidation and interpretation of the available information on B12 nutrition. Historically, most focus has been on diagnosis and treatment of clinical symptoms of B12 deficiency, which result primarily from pernicious anemia or strict vegetarianism. More recently, we have become aware of the high prevalence of B12 insufficiency in populations consuming low amounts of animal-source foods, which can be detected with ≥1 serum biomarker but presents the new challenge of identifying functional consequences that may require public health interventions.
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Affiliation(s)
- Lindsay H Allen
- USDA, Agricultural Research Service Western Human Nutrition Research Center, University of California, Davis, CA
| | - Joshua W Miller
- Department of Nutritional Sciences, Rutgers University, New Brunswick, NJ
| | - Lisette de Groot
- Division of Human Nutrition, Wageningen University, Wageningen, Netherlands
| | - Irwin H Rosenberg
- Friedman School of Nutrition Science and Policy, Tufts University, Boston, MA
| | - A David Smith
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Helga Refsum
- Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Daniel J Raiten
- Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD
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Griffioen PH, van Dam-Nolen DHK, Lindemans J, Heil SG. Measurement of total Transcobalamin employing a commercially available assay for Active B12. Clin Biochem 2017; 50:1030-1033. [PMID: 28823760 DOI: 10.1016/j.clinbiochem.2017.08.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Revised: 08/15/2017] [Accepted: 08/16/2017] [Indexed: 11/17/2022]
Abstract
INTRODUCTION Vitamin B12 deficiency is mostly caused by insufficient gastro-intestinal absorption and in rare conditions by Transcobalamin (TC) deficiency. Unsaturated Transcobalamin (apoTC) can be measured by a binding assay using radiolabeled cobalamin. The Active B12 test analyzes saturated Transcobalamin (holoTC) and we hypothesize that this test can be used to measure total TC by additional in vitro saturation with cobalamin. METHODS Serum was saturated in vitro (16 times dilution) with a cyanocobalamin solution and total TC was selectively measured with the Abbott Active B12 test. ApoTC was calculated by subtracting endogenous holoTC from total TC after correction for dilution. Linearity was determined with a pool serum dilution series. Precision was investigated according to the CLSI EP15 protocol. Method comparison was performed against a binding assay using radiolabeled cobalamin. Reference values were determined in 100 healthy controls. RESULTS The method was linear in the range of 240 to 1933pmol/L (R2=0.997, lack of fit F=1.61). Precision of low- and high-pool total TC in serum were; 5.2% and 4.3% respectively. Method comparison against a radiolabeled cobalamin binding assay showed a proportional bias of 30% (y=0.70x+126). Total TC reference values were determined at 500-1276pmol/L. CONCLUSION We describe a rapid method to quantify total TC, which can be implemented on routine platforms using commercial Active B12 tests. In addition, apoTC can be assessed by subtracting endogenous holoTC concentration which can be measured in the same run, securing the same calibration level for all three parameters (holoTC, apoTC and total TC). This method is applicable in clinical diagnostics and in larger epidemiological studies.
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Affiliation(s)
- Pieter H Griffioen
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands
| | - Dianne H K van Dam-Nolen
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands
| | - Jan Lindemans
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands
| | - Sandra G Heil
- Erasmus MC University Medical Center Rotterdam, Department of Clinical Chemistry, PO box 2040, 3000 CA Rotterdam, The Netherlands.
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Green R, Allen LH, Bjørke-Monsen AL, Brito A, Guéant JL, Miller JW, Molloy AM, Nexo E, Stabler S, Toh BH, Ueland PM, Yajnik C. Vitamin B 12 deficiency. Nat Rev Dis Primers 2017; 3:17040. [PMID: 28660890 DOI: 10.1038/nrdp.2017.40] [Citation(s) in RCA: 432] [Impact Index Per Article: 61.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Vitamin B12 (B12; also known as cobalamin) is a B vitamin that has an important role in cellular metabolism, especially in DNA synthesis, methylation and mitochondrial metabolism. Clinical B12 deficiency with classic haematological and neurological manifestations is relatively uncommon. However, subclinical deficiency affects between 2.5% and 26% of the general population depending on the definition used, although the clinical relevance is unclear. B12 deficiency can affect individuals at all ages, but most particularly elderly individuals. Infants, children, adolescents and women of reproductive age are also at high risk of deficiency in populations where dietary intake of B12-containing animal-derived foods is restricted. Deficiency is caused by either inadequate intake, inadequate bioavailability or malabsorption. Disruption of B12 transport in the blood, or impaired cellular uptake or metabolism causes an intracellular deficiency. Diagnostic biomarkers for B12 status include decreased levels of circulating total B12 and transcobalamin-bound B12, and abnormally increased levels of homocysteine and methylmalonic acid. However, the exact cut-offs to classify clinical and subclinical deficiency remain debated. Management depends on B12 supplementation, either via high-dose oral routes or via parenteral administration. This Primer describes the current knowledge surrounding B12 deficiency, and highlights improvements in diagnostic methods as well as shifting concepts about the prevalence, causes and manifestations of B12 deficiency.
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Affiliation(s)
- Ralph Green
- Department of Pathology and Laboratory Medicine, University of California Davis, 4400 V Street, PATH Building, Davis, California 95817, USA
| | - Lindsay H Allen
- USDA, ARS Western Human Nutrition Research Center, University of California Davis, Davis, California, USA
| | | | - Alex Brito
- USDA, ARS Western Human Nutrition Research Center, University of California Davis, Davis, California, USA
| | - Jean-Louis Guéant
- Inserm UMRS 954 N-GERE (Nutrition Génétique et Exposition aux Risques Environnementaux), University of Lorraine and INSERM, Nancy, France
| | - Joshua W Miller
- School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey, USA
| | - Anne M Molloy
- School of Medicine and School of Biochemistry and Immunology, Trinity College Dublin, University of Dublin, Dublin, Ireland
| | - Ebba Nexo
- Department of Clinical Medicine, Clinical Biochemistry, Aarhus University Hospital, Aarhus, Denmark
| | - Sally Stabler
- Department of Medicine, University of Colorado Denver, Denver, Colorado, USA
| | - Ban-Hock Toh
- Centre for Inflammatory Diseases, Monash Institute of Medical Research, Clayton, Victoria, Australia
| | - Per Magne Ueland
- Laboratory of Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway.,Section for Pharmacology, Department of Clinical Science, University of Bergen, Bergen, Norway
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Devalia V, Hamilton MS, Molloy AM. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol 2014; 166:496-513. [PMID: 24942828 DOI: 10.1111/bjh.12959] [Citation(s) in RCA: 222] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The clinical picture is the most important factor in assessing the significance of test results assessing cobalamin status because there is no 'gold standard' test to define deficiency. Serum cobalamin currently remains the first-line test, with additional second-line plasma methylmalonic acid to help clarify uncertainties of underlying biochemical/functional deficiencies. Serum holotranscobalamin has the potential as a first-line test, but an indeterminate 'grey area' may still exist. Plasma homocysteine may be helpful as a second-line test, but is less specific than methylmalonic acid. The availability of these second-line tests is currently limited. Definitive cut-off points to define clinical and subclinical deficiency states are not possible, given the variety of methodologies used and technical issues, and local reference ranges should be established. In the presence of discordance between the test result and strong clinical features of deficiency, treatment should not be delayed to avoid neurological impairment. Treatment of cobalamin deficiency is recommended in line with the British National Formulary. Oral therapy may be suitable and acceptable provided appropriate doses are taken and compliance is not an issue. Serum folate offers equivalent diagnostic capability to red cell folate and is the first-line test of choice to assess folate status.
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Hooper M, Hudson P, Porter F, McCaddon A. Patient journeys: diagnosis and treatment of pernicious anaemia. ACTA ACUST UNITED AC 2014; 23:376-81. [DOI: 10.12968/bjon.2014.23.7.376] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Fiona Porter
- Member/Trustee, The Pernicious Anaemia Society, Bridgend
| | - Andrew McCaddon
- Senior Honorary Research Fellow, Cardiff University, School of Medicine, Wrexham Technology Park, Wrexham
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Gupta PK, Garg RK, Gupta RK, Malhotra HS, Paliwal VK, Rathore RKS, Verma R, Singh MK, Rai Y, Pandey CM. Diffusion tensor tractography and neuropsychological assessment in patients with vitamin B12 deficiency. Neuroradiology 2013; 56:97-106. [DOI: 10.1007/s00234-013-1306-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 11/28/2013] [Indexed: 11/30/2022]
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Remacha AF, Sardà MP, Canals C, Queraltò JM, Zapico E, Remacha J, Carrascosa C. Role of serum holotranscobalamin (holoTC) in the diagnosis of patients with low serum cobalamin. Comparison with methylmalonic acid and homocysteine. Ann Hematol 2013; 93:565-9. [PMID: 24057896 DOI: 10.1007/s00277-013-1905-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 09/10/2013] [Indexed: 10/26/2022]
Abstract
Plasma holotranscobalamin (holoTC) transports active cobalamin. Decreased levels of holoTC have been considered to be the earliest marker of cobalamin (Cbl) deficiency. In this work, holoTC was evaluated in low or borderline serum Cbl (LB12) and a concordance analysis was carried out with methylmalonic acid (MMA) and homocysteine (Hcy). Levels of Cbl, holoTC, MMA, and Hcy were investigated in a reference group in 106 patients with LB12 (≤200 pmol/l) and in 27 with folate deficiency (FOL). HoloTC levels were evaluated by an automated immunoassay (Active B12, Abbott Lab, Abbott Park, IL, USA). Lower levels of holoTC were observed in both LB12 and FOL groups (reference group vs LB12; p < 0.0001. Reference group vs FOL; p = 0.002). HoloTC levels were lower in LB12 than in FOL (p = 0.001). In LB12, concordance between Hcy and MMA was 82.1 % (chi-square test, p < 0.001; Kappa Index, 0.64, p < 0.0001). Concordance between Hcy and holoTC was 62 % (chi-square test, p = 0.006; Kappa index, 0.245, p = 0.006). Concordance between holoTC and MMA was 55.6 % (p = 0.233). Some cases with LB12 and elevated MMA did not show decreased holoTC. By contrast, MMA and Hcy were not increased in some patients with low holoTC and LB12. In conclusion, levels of holoTC were decreased in LB12 and FOL. In LB12 patients, holoTC concordance with MMA was poor. MMA/Hcy levels were not increased in a significant number of subjects with LB12 and low holoTC. This profile was found in iron deficiency. The significance of these changes remains to be clarified.
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Affiliation(s)
- A F Remacha
- Hematology Department, Hospital de Sant Pau, Avda Padre Claret 167, Barcelona, 08025, Spain,
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Carmel R. Diagnosis and management of clinical and subclinical cobalamin deficiencies: why controversies persist in the age of sensitive metabolic testing. Biochimie 2013; 95:1047-55. [PMID: 23416723 DOI: 10.1016/j.biochi.2013.02.008] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2013] [Accepted: 02/08/2013] [Indexed: 01/11/2023]
Abstract
In the past two decades, sensitive biochemical tests have uncovered cobalamin deficiency much more frequently than ever before. Almost all cases involve mild, biochemical changes without clinical manifestations (subclinical cobalamin deficiency; SCCD), whose health impact is unclear. Because the causes of SCCD are most often unknown, nonmalabsorptive, and seldom documented, controversy and confusion surround the diagnostic criteria and, inevitably, consequences and management of SCCD. To complicate matters, our grasp of the rarer clinical deficiency, usually a serious, progressive medical disease rooted in severe malabsorption, has receded as absorption testing has disappeared. Reexamining the accumulation of assumptions and misperceptions about cobalamin deficiency and distinguishing SCCD from clinical deficiency is long overdue. The biology of cobalamin provides an important starting point: cobalamin stores exceed daily losses so greatly and binding proteins regulate absorption so effectively that deficiency typically achieves clinical expression only after years of severe, relentless malabsorption. Dietary insufficiency, mild, partial malabsorption, and other incomplete, intermittent causes can usually produce only SCCD. Thus, the most fundamental difference between the two deficiencies is the relentlessness of the underlying cause, which determines prognosis and health impact. Inattention to absorptive status has exacerbated the limitations of biochemical testing. All the biochemical tests are highly sensitive but specificity is poor, no diagnostic gold standard exists, and diagnostic cutpoints fluctuate excessively. To limit the adverse diagnostic consequences, the diagnosis of SCCD, whose need for treatment is unclear, should be deferred unless at least two tests are abnormal. Indeed, cobalamin biology indicates that the absorption system, while enhancing cobalamin delivery, also sets a strict upper limit on it, which suggests that cobalamin excess is undesirable. Solving cobalamin deficiency requires balanced assessment of the different imperatives of clinical and public health concerns, better rationalization of diagnostic testing, consistent definitions of normality in relation to SCCD, and rational cutpoint selection.
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Affiliation(s)
- Ralph Carmel
- Department of Medicine, New York Methodist Hospital, Brooklyn, NY, USA.
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Abstract
Vitamin B(12) (B(12); also known as cobalamin) is a cofactor in many metabolic processes; deficiency of this vitamin is associated with megaloblastic anaemia and various neurological disorders. In contrast to many prokaryotes, humans and other mammals are unable to synthesize B(12). Instead, a sophisticated pathway for specific uptake and transport of this molecule has evolved. Failure in the gastrointestinal part of this pathway is the most common cause of nondietary-induced B(12) deficiency disease. However, although less frequent, defects in cellular processing and further downstream steps in the transport pathway are also known culprits of functional B(12) deficiency. Biochemical and genetic approaches have identified novel proteins in the B(12) transport pathway--now known to involve more than 15 gene products--delineating a coherent pathway for B(12) trafficking from food to the body's cells. Some of these gene products are specifically dedicated to B(12) transport, whereas others embrace additional roles, which explains the heterogeneity in the clinical picture of the many genetic disorders causing B(12) deficiency. This Review describes basic and clinical features of this multistep pathway with emphasis on gastrointestinal transport of B(12) and its importance in clinical medicine.
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Abstract
PURPOSE OF REVIEW This review focuses on recent developments and controversies in the diagnosis, consequences, and management of subclinical cobalamin deficiency (SCCD), which affects many elderly persons. RECENT FINDINGS Diagnosis of SCCD depends exclusively on biochemical tests whose individual limitations suggest that combinations of tests are needed, especially in epidemiologic research. The causes of SCCD are unknown in more than 60% of cases, which limits prognostic predictions and identification of health consequences. After years of varying, often inconclusive associations, new clinical trials suggest that homocysteine reduction by high doses of folic acid, cobalamin, and pyridoxine may reduce progression of structural brain changes and cognitive impairment, especially in predisposed individuals. The causative or contributory roles, if any, of SCCD itself in cognitive dysfunction require direct study. If the findings are confirmed, high-dose supplementation with three vitamins will probably be more effective than fortification of the diet. SUMMARY The story of SCCD, which is severalfold times more common in the elderly than clinical cobalamin deficiency but also differs from it in arising only infrequently from severe malabsorption and thus being less likely to progress, continues to evolve. Preventive benefits need to be confirmed and expanded, and will require fuller understanding of SCCD pathophysiology, natural history, and health consequences.
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Greibe E, Nexo E. Vitamin B12 absorption judged by measurement of holotranscobalamin, active vitamin B12: evaluation of a commercially available EIA kit. Clin Chem Lab Med 2011; 49:1883-5. [PMID: 21995605 DOI: 10.1515/cclm.2011.754] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND Active vitamin B12 absorption is followed by an increase in holotranscobalamin (holoTC) upon loading with a high physiological dose of the vitamin (the CobaSorb test). This study evaluates the use of a newly launched EIA kit for measurement of holoTC (active B12) in relation to the CobaSorb test. METHODS Intra-assay imprecision and linearity of the EIA kit was examined, employing serum pools of increasing holoTC concentrations. For the CobaSorb test, holoTC was measured before and after loading with 3-times 9 μg of vitamin B12 employing both the in-house ELISA and the EIA kit (n=25). RESULTS The EIA kit showed an intra-assay CV between 2.2% and 5.8% for holoTC values ranging from 21 to 80 pmol/L. Employing diluted serum samples resulted in spurious high values of holoTC. The EIA kit performed well in relation to the CobaSorb test and classified the patients studied as capable of absorbing vitamin B12 (n=10) or not (n=15), as did the in-house ELISA. CONCLUSIONS The Active B12 (holoTC) EIA kit proved suitable for use with the CobaSorb test, but not for analysis of diluted serum samples.
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Affiliation(s)
- Eva Greibe
- Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus, Denmark
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