Detection of Vitamin B12 Deficiency in Older People by Measuring Vitamin B12 or the Active Fraction of Vitamin B12, Holotranscobalamin

Clinical Pathobiochemistry of Vitamin B12 Deficiency: Improving Our Understanding by Exploring Novel Mechanisms with a Focus on Diabetic Neuropathy

Vitamin B₁₂ (B₁₂) is an essential cofactor of two important biochemical pathways, the degradation of methylmalonic acid and the synthesis of methionine from homocysteine. Methionine is an important donor of methyl groups for numerous biochemical reactions, including DNA synthesis and gene regulation. Besides hematological abnormalities (megaloblastic anemia or even pancytopenia), a deficiency in B₁₂ may cause neurological symptoms, including symptoms resembling diabetic neuropathy. Although extensively studied, the underlining molecular mechanism for the development of diabetic peripheral neuropathy (DPN) is still unclear. Most studies have found a contribution of oxidative stress in the development of DPN. Detailed immunohistochemical investigations in sural nerve biopsies obtained from diabetic patients with DPN point to an activation of inflammatory pathways induced via elevated advanced glycation end products (AGE), ultimately resulting in increased oxidative stress. Similar results have been found in patients with B₁₂ deficiency, indicating that the observed neural changes in patients with DPN might be caused by cellular B₁₂ deficiency. Since novel results show that B₁₂ exerts intrinsic antioxidative activity in vitro and in vivo, B₁₂ may act as an intracellular, particularly as an intramitochondrial, antioxidant, independent from its classical, well-known cofactor function. These novel findings may provide a rationale for the use of B₁₂ for the treatment of DPN, even in subclinical early states.

Vitamin B12 deficiency: correction of P-methylmalonic acid for estimated glomerular filtration rate to improve diagnostic value - a confirmatory study

Objectives: For diagnosis of vitamin B12 deficiency, plasma methylmalonic acid (P-MMA) is considered superior to plasma vitamin B12 (P-B12). Reduced kidney function elevates P-MMA, hence, hampering P-MMA as a biomarker. We assessed whether correcting P-MMA for estimated glomerular filtration rate (eGFR) can affect the estimated prevalence of B12 deficiency. Methods: We included 115,245 patients with concomitant measurements of P-MMA, P-B12 and P-Creatinine. B12 deficiency was classified using P-MMA decision limits at >0.75 and >0.43 µmol/L. The non-linear relation between eGFR and P-MMA was estimated using spline regression. We calculated the percentage-wise reclassification of B12 deficiency by using an eGFR corrected P-MMA formula with eGFR reference points of 90 and 60 mL/min. Results: 6% with B12 deficiency were reclassified as non-deficient after adjusting for eGFR (reference point eGFR 90 mL/min) with both P-MMA decision limits. Overall B12 deficiency prevalence was reduced from 9.6% to 9.0% (P-MMA decision limit 0.43 µmol/L). With P-MMA decision limits at 0.75 and 0.43 µmol/L, 33.6% and 44.8% of B12 deficient patients with an eGFR <60 mL/min were reclassified as non-deficient. Conclusions: We have demonstrated that correcting P-MMA for eGFR can reclassify P-MMA levels across decision limits for diagnosing B12 deficiency, in particular for patients with reduced kidney function. This may have clinical implications for avoiding overdiagnosis of this chronic disease.

Diagnostic and Therapeutic Perspectives Associated to Cobalamin-Dependent Metabolism and Transcobalamins’ Synthesis in Solid Cancers

Cobalamin or vitamin B12 (B12) is a cofactor for methionine synthase and methylmalonyl-CoA mutase, two enzymes implicated in key pathways for cell proliferation: methylation, purine synthesis, succinylation and ATP production. Ensuring these functions in cancer cells therefore requires important cobalamin needs and its uptake through the transcobalamin II receptor (TCII-R). Thus, both the TCII-R and the cobalamin-dependent metabolic pathways constitute promising therapeutic targets to inhibit cancer development. However, the link between cobalamin and solid cancers is not limited to cellular metabolism, as it also involves the circulating transcobalamins I and II (TCI or haptocorrin and TCII) carrier proteins, encoded by TCN1 and TCN2, respectively. In this respect, elevations of B12, TCI and TCII concentrations in plasma are associated with cancer onset and relapse, and with the presence of metastases and worse prognosis. In addition, TCN1 and TCN2 overexpressions are associated with chemoresistance and a proliferative phenotype, respectively. Here we review the involvement of cobalamin and transcobalamins in cancer diagnosis and prognosis, and as potential therapeutic targets. We further detail the relationship between cobalamin-dependent metabolic pathways in cancer cells and the transcobalamins’ abundancies in plasma and tumors, to ultimately hypothesize screening and therapeutic strategies linking these aspects.

Personalising laboratory medicine in the 'real world': Assessing clinical utility, by clinical indication, of serum total B12 and Active-B12® (holotranscobalamin) in the diagnosis of vitamin B12 deficiency

BACKGROUND

Assessing the pre- and post-test probability of disease in the context of routine health care is challenging. We wished to study how test performance parameters relating to clinical utility vary by clinical indication in a 'real-world' setting.

METHODS

The diagnostic accuracy of serum total B12 and Active-B12® (holotranscobalamin) was evaluated in a primary care population, using serum methylmalonic acid as the reference standard. We used electronic requesting to establish the clinical indication for each request. Routine requests from primary care for serum total B12 were included if creatinine was also measured and estimated glomerular filtration rate was at least 60 mL/min/1.73 m2.

RESULTS

Clinical indications included peripheral neuropathy (n = 168), anaemia (n = 168), cognitive decline (n = 125), suspected dietary deficiency (n = 76), other (n = 362). For peripheral neuropathy, the area under the receiver operator curve ± 95% confidence interval (AUC ± CI) was 0.63 (0.54-0.71) (P = 0.002) for total B12 and 0.68 (0.60-0.77) (P < 0.0001) for Active-B12®. For anaemia, AUC ± CI was 0.56 (0.47-0.66) (P = 0.10) for total B12 and 0.69 (0.59-0.78) (P < 0.0001) for Active-B12®. For cognitive decline, AUC ± CI was 0.54 (0.43-0.65) (P = 0.26) for total B12 and 0.69 (0.58-0.80) (P = 0.0002) for Active-B12®. The pre-post-test change in probability of disease varied by clinical indication.

CONCLUSION

Combining diagnostic accuracy studies and electronic testing in a 'real-world' setting allows clinical utility to be assessed by clinical indication. Wider application of this would permit more personalised laboratory medicine. In this study, diagnostic performance of total B12 and Active-B12® varied across all indications. Active-B12® provided better discrimination, but this may have reflected the cut-offs used.

Assessment of Vitamin B12 Deficiency and Risk Factors in Healthy Infants

OBJECTIVE

To study vitamin B₁₂ deficiency in apparently healthy infants and their mothers and assess the risk factors.

METHODS

A hospital-based, cross-sectional, observational study was conducted from July 2016 through December 2017. Consecutive healthy and normally developing infants were enrolled. Red blood cell folate, plasma vitamin B₁₂, homocysteine and methylmalonic acid levels of mothers and infants were assessed.

RESULTS

Seventy-four healthy infants were enrolled. Male-to-female ratio was 1.5:1. Anemia in 66.2% (n = 49), low plasma B₁₂ in 17.6% (n = 13), hyperhomocysteinemia in 48.6% (n = 36), plasma methylmalonic acid in 100% (n = 74) and 'confirmed' B₁₂ deficiency in 38% (n = 28) infants were noted. The proportion of hyperhomocysteinemia increased to 75.7% (n = 56) infants using a lower cut-off of >10 μmol/L. In mothers, low B₁₂ in 19%, hyperhomocysteinemia in 57% and elevated plasma methylmalonic acid in 100% were noted. Median plasma B₁₂ level was 314 pg/ml (IQR 221-421), median plasma homocysteine 15.4 μmol/L (IQR 11.3-21.7) and median plasma methylmalonic acid was 8.28 μmol/L (IQR 4.4-13.1) in mothers. Folate deficiency was noted in 9.4% infants and 12% of mothers. Overall, 63.5% mothers were vegetarian and, 64% of the mothers of infants with confirmed vitamin B12 deficiency were pure vegetarians. Odds of developing vitamin B₁₂ deficiency increased by more than 5 times in those whose mothers' serum vitamin B₁₂ levels were low as compared to normal maternal vitamin B₁₂ levels (OR 5.42; 95% CI: 1.96-16.6; p 0.002).

CONCLUSIONS

There is a high prevalence of vitamin B₁₂ deficiency in infants and their mothers. There is urgent need to supplement our population with vitamin B₁₂.

Assessing Diagnostic Accuracy of Serum Holotranscobalamin (Active-B12) in Comparison with Other Markers of Vitamin B12 Deficiency

About 15-40% India is Vitamin B12 deficient (commonly diagnosed by total Vitamin B12) but, as only holoTC (active form) is taken up by body cells, thus measuring holoTC is more reflective of Vitamin B12 status than the former. We aimed to assess diagnostic accuracy of serum holoTC in comparison with total Vitamin B12 and total Homocysteine (HCY) as indicator of serum Vitamin B12 status. 217 human subjects (99 males and 118 females) ranging from 17 to 83 years were divided into Vitamin B12 deficient (n = 70), borderline (n = 100) and sufficient groups (n = 47) who were further assessed for markers of Vitamin B12 deficiency-holoTC, HCY, Mean Corpuscular Volume (MCV), Folate, heamoglobin and creatinine. Samples were analysed using Siemens Advia Centaur Xpi. Total Vitamin B12 deficient group had - 84.3% holoTC deficient; 15.7% holoTC sufficient; 72.9% with elevated HCY; 27.1% with normal HCY; 11.4% with megaloblastic anaemia. Borderline group had - 34% holoTC deficient; 28% elevated HCY. A strong positive correlation was found between Total Vitamin B12 and holoTC (r = 0.754, p = <0.001) but strong negative correlation existed between holoTC and HCY (r = - 0.471, p = <0.001). Concordance between Total Vit B12 and HCY (Kappa index = 0.51, p < 0.001); between holoTC and HCY (Kappa index = 0.52, p = <0.001) were statically significant but the latter had a better sensitivity and specificity. Also, statically significant association exists between Total Vitamin B12 and holoTC with HCY (p = <0.001). Therefore, it is ascertained that Active Vitamin B12 assay is a better test and can be considered as an early marker of vitamin B12 deficiency.

Vitamin B12 Status and Optimal Range for Hemoglobin Formation in Elite Athletes

Background: Athletes and coaches believe in the ergogenic effect of vitamin B₁₂ (which results from enhanced erythropoiesis) and they often insist on its unjustified supplementation. Therefore, our study aimed to assess the vitamin B₁₂ status in Polish elite athletes and its influence on red blood cell parameters. Methods: In total, 1131 blood samples were collected during six years from 243 track and field athletes divided into strength and endurance groups, as well as according to the declared use of vitamin B₁₂ injections. Results: An average vitamin B₁₂ concentration in all subjects was 739 ± 13 pg/mL, with no cases of deficiency. A weak but significant relationship was found between vitamin B₁₂ and hemoglobin concentrations. A significant increase in hemoglobin appeared from very low vitamin B₁₂ concentration and up to approx. 400 pg/mL, while hemoglobin did not significantly change from 700 pg/mL and onwards. Vitamin B₁₂ injections were used by 34% of athletes, significantly more often by endurance than by strength athletes. In athletes who declared no use of injections, a higher concentration of vitamin B₁₂ was observed in the endurance group. Conclusion: The main finding of the present study is the determination of the range of vitamin B₁₂ concentration which may favor better hemoglobin synthesis in athletes. They should regularly monitor vitamin B₁₂ concentration and maintain the range of 400–700 pg/mL as it may improve red blood cell parameters. We might suggest application of a supplementation if necessary. Special attention is required in athletes with a vitamin B₁₂ concentration below 400 pg/mL.

In-vivo Intradermal Delivery of Co-57 labeled Vitamin B-12, and Subsequent Comparison with Standard Subcutaneous Administration

Vitamin B-12 (cobalamin) deficiency in humans is a worldwide problem emanating from varied causes such as insufficient dietary intake or malabsorption of the micronutrient due to an underlying condition (absence or failure of intrinsic factor, atrophic gastritis, post-operative bariatric surgery, inflammatory bowel disease, cobalt deficiency etc.). As oral supplementation is limited by its bioavailability due to the absorptive property of intrinsic factor, clinicians often prescribe parenteral forms of administration to replenish diminished levels rapidly. The gold standard in parenteral delivery of cobalamin is subcutaneous and/or intramuscular injections. The relatively large molecular size of cobalamin (1355.39 Da) makes passive transdermal patch-based delivery via the stratum corneum quite challenging. Hence, the primary goal of this study is to investigate the feasibility of intradermal (ID) delivery of Vitamin B-12 via an almost painless microneedle injection and subsequent comparison with standard subcutaneous (SC) delivery. This work reports on a custom-made microneedle device built from a commercial insulin needle and it's use to perform ID delivery of Co-57 radiolabeled Vitamin B-12 in-vivo in rabbits. The pharmacokinetic profile and bioavailability were studied and compared with SC delivery. It is the first comprehensive study, to our best knowledge, that compares a micronutrient (eg. Vitamin B-12) delivery via ID and SC routes in-vivo. While the bioavailability for the SC route is found to be slightly higher compared to the ID route (99% vs. 96%), the T_max for both are almost identical. Thus, ID delivery of Vitamin B-12 using a microneedle injection could be a viable and minimally invasive alternative to existing parenteral options.

Voluntary fortification is ineffective to maintain the vitamin B12 and folate status of older Irish adults: evidence from the Irish Longitudinal Study on Ageing (TILDA)

Mandatory fortification of staple grains with folic acid and/or vitamin B12 (B12) is under debate in many countries including Ireland, which has a liberal, but voluntary, fortification policy. Older adults can be at risk of both deficiency and high folate status, although little is known on the actual prevalence and the major predictors. Population prevalence estimates from older adults (n 5290 ≥50 years) from the Irish Longitudinal Study on Ageing (TILDA) (Wave 1) are presented here. Measures included plasma total vitamin B12 and folate, whereas predictors included detailed demographic, socio-economic, geographic, seasonal and health/lifestyle data. The prevalence of deficient or low B12 status (45 nmol/l) was observed in 8·9 %, whereas high B12 status was observed in 3·1 % (>601 pmol/l). The largest positive predictor of B12 concentration was self-reported B12 injection and/or supplement use (coefficient 51·5 pmol/; 95 % CI 9·4, 93·6; P=0·016) followed by sex and geographic location. The largest negative predictor was metformin use (-33·6; 95 % CI -51·9, -15·4; P<0·0001). The largest positive predictor of folate concentration was folic acid supplement use (6·0; 95 % CI 3·0, 9·0 nmol/l; P<0·001) followed by being female and statin medications. The largest negative predictor was geographic location (-5·7; 95 % CI -6·7, -4·6; P<0·0001) followed by seasonality and smoking. B-vitamin status in older adults is affected by health and lifestyle, medication, sampling period and geographic location. We observed a high prevalence of low B12 and folate status, indicating that the current policy of voluntary fortification is ineffective for older adults.

Vitamin B12 Intake From Animal Foods, Biomarkers, and Health Aspects

The EAT-Lancet commission recently suggested that transformation to healthy diets by 2050 will require a reduction of at least 50% in consumption of foods such as red meat and sugar, and a doubling in the global consumption of fruits, vegetables, nuts, and legumes. A diet rich in plant-based foods and with fewer animal source foods confers both improved health and environmental benefits. Notably, the risk of vitamin B12 deficiency increases when consuming a diet low in animal products. Humans are dependent on animal foods such as dairy products, meat, fish and eggs. Vitamin B12 deficiency is common worldwide, especially in populations with low consumption of animal foods because of low socioeconomic status, ethical reasons, or because of their lifestyle (i.e., vegans). According to the European Food Safety Authoroty, the recommended adequate intake of vitamin B12 is 4.0 μg/d for adults, and vitamin B12 requirements are higher during pregnancy and lactation. Infants and children from deficient mothers and elderly people are at risk for vitamin B12 deficiency. Diagnosis of vitamin B12 deficiency is hampered by low specificity of available biomarkers, and there is no consensus yet regarding the optimal definition of low vitamin B12 status. In general, a combination of at least two biomarkers is recommended. Therefore, this review presents an overview of vitamin B12 biochemistry and its biomarkers. We further summarize current recommendations of vitamin B12 intake, and evidence on the associations of vitamin B12 intake from different nutrient-dense animal foods with vitamin B12 status markers. Finally, potential consequences of low vitamin B12 status on different health outcomes for pregnant women, infants and elderly are presented.

B-vitamins and body composition: integrating observational and experimental evidence from the B-PROOF study

Purpose

Higher folate and vitamin-B12 have been linked to lower risk of overweight. However, whether this is a causal effect of these B-vitamins on obesity risk remains unclear and evidence in older individuals is scarce. This study aimed to assess the role of B-vitamin supplementation and levels on body composition in older individuals.

Methods

A double-blind, randomized controlled trial in 2919 participants aged ≥ 65 years with elevated homocysteine levels. The intervention comprised a 2-year supplementation with a combination of folic acid (400 µg) and vitamin B12 (500 µg), or with placebo. Serum folate, vitamin-B12, active vitamin-B12 (HoloTC), methylmalonic acid (MMA), and anthropometrics were measured at baseline and after 2 years of follow-up. Dietary intake of folate and vitamin-B12 was measured at baseline in a subsample (n = 603) using a validated food-frequency questionnaire. Fat mass index (FMI) and fat-free mass index (FFMI) were assessed with Dual Energy X-ray absorptiometry (DXA).

Results

Cross-sectional analyses showed that a 1 nmol/L higher serum folate was associated with a 0.021 kg/m² lower BMI (95% CI − 0.039; − 0.004). Higher HoloTC (per pmol/L log-transformed) was associated with a 0.955 kg/m² higher FMI (95% CI 0.262; 1.647), and higher MMA (per μgmol/L) was associated with a 1.108 kg/m² lower FMI (95% CI − 1.899; − 0.316). However, random allocation of B-vitamins did not have a significant effect on changes in BMI, FMI or FFMI during 2 years of intervention.

Conclusions

Although observational data suggested that folate and vitamin B12 status are associated with body composition, random allocation of a supplement with both B-vitamins combined versus placebo did not confirm an effect on BMI or body composition.

Electronic supplementary material

The online version of this article (10.1007/s00394-019-01985-8) contains supplementary material, which is available to authorized users.

The Effect of Whey and Soy Protein Isolates on Cognitive Function in Older Australians with Low Vitamin B12: A Randomised Controlled Crossover Trial

Whey protein isolate (WPI) is high in vitamin B₁₂ and folate. These and other related markers (holotranscobalamin, methylmalonic acid and homocysteine) have been linked with cognitive health. This study explored the efficacy of WPI for improving cognitive function via delivery of vitamin B₁₂. Moderately vitamin B₁₂-deficient participants aged between 45 and 75 years (n = 56) were recruited into this randomised controlled crossover trial. Participants (55% female) consumed 50 g whey (WPI; active) or soy protein isolate (SPI; control) for eight weeks. Following a 16-week washout phase, they consumed the alternative supplement. Consumption of WPI significantly improved active B₁₂ and folate status but did not result in direct improvements in cognitive function. However, there was evidence of improvement in reaction time (p = 0.02) and reasoning speed (p = 0.04) in the SPI condition for females. Additional analyses showed that changes in active B₁₂, HcY and folate measures during WPI treatment correlated with improvements in cognitive function (all p < 0.05). Results indicate that WPI itself did not result in improved cognitive function but some evidence of benefit of SPI for females was found. However, consistent with previous research, we present further evidence of a role for active B₁₂, HcY and folate in supporting cognitive improvement in adults with low B vitamin status.

Expression of TCN1 in Blood is Negatively Associated with Verbal Declarative Memory Performance

Memory is indispensable for normal cognitive functioning, and the ability to store and retrieve information is central to mental health and disease. The molecular mechanisms underlying complex memory functions are largely unknown, but multiple genome-wide association studies suggest that gene regulation may play a role in memory dysfunction. We performed a global gene expression analysis using a large and balanced case-control sample (n = 754) consisting of healthy controls and schizophrenia and bipolar disorder patients. Our aim was to discover genes that are differentially expressed in relation to memory performance. Gene expression in blood was measured using Illumina HumanHT-12 v4 Expression BeadChip and memory performance was assessed with the updated California Verbal Learning Test (CVLT-II). We found that elevated expression of the vitamin B12-related gene TCN1 (haptocorrin) was significantly associated with poorer memory performance after correcting for multiple testing (β = −1.50, p = 3.75e-08). This finding was validated by quantitative real-time PCR and followed up with additional analyses adjusting for confounding variables. We also attempted to replicate the finding in an independent case-control sample (n = 578). The relationship between TCN1 expression and memory impairment was comparable to that of important determinants of memory function such as age and sex, suggesting that TCN1 could be a clinically relevant marker of memory performance. Thus, we identify TCN1 as a novel genetic finding associated with poor memory function. This finding may have important implications for the diagnosis and treatment of vitamin B12-related conditions.

Vitamin B12 deficiency

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.

Identification and Quantitation of Malonic Acid Biomarkers of In-Born Error Metabolism by Targeted Metabolomics

Malonic acid (MA), methylmalonic acid (MMA), and ethylmalonic acid (EMA) metabolites are implicated in various non-cancer disorders that are associated with inborn-error metabolism. In this study, we have slightly modified the published 3-nitrophenylhydrazine (3NPH) derivatization method and applied it to derivatize MA, MMA, and EMA to their hydrazone derivatives, which were amenable for liquid chromatography- mass spectrometry (LC-MS) quantitation. 3NPH was used to derivatize MA, MMA, and EMA, and multiple reaction monitoring (MRM) transitions of the corresponding derivatives were determined by product-ion experiments. Data normalization and absolute quantitation were achieved by using 3NPH derivatized isotopic labeled compounds ¹³C₂-MA, MMA-D₃, and EMA-D₃. The detection limits were found to be at nanomolar concentrations and a good linearity was achieved from nanomolar to millimolar concentrations. As a proof of concept study, we have investigated the levels of malonic acids in mouse plasma with malonyl-CoA decarboxylase deficiency (MCD-D), and we have successfully applied 3NPH method to identify and quantitate all three malonic acids in wild type (WT) and MCD-D plasma with high accuracy. The results of this method were compared with that of underivatized malonic acid standards experiments that were performed using hydrophilic interaction liquid chromatography (HILIC)-MRM. Compared with HILIC method, 3NPH derivatization strategy was found to be very efficient to identify these molecules as it greatly improved the sensitivity, quantitation accuracy, as well as peak shape and resolution. Furthermore, there was no matrix effect in LC-MS analysis and the derivatized metabolites were found to be very stable for longer time. Graphical Abstract ᅟ.

Vitamin B12 deficiency from the perspective of a practicing hematologist

B₁₂ deficiency is the leading cause of megaloblastic anemia, and although more common in the elderly, can occur at any age. Clinical disease caused by B₁₂ deficiency usually connotes severe deficiency, resulting from a failure of the gastric or ileal phase of physiological B₁₂ absorption, best exemplified by the autoimmune disease pernicious anemia. There are many other causes of B₁₂ deficiency, which range from severe to mild. Mild deficiency usually results from failure to render food B₁₂ bioavailable or from dietary inadequacy. Although rarely resulting in megaloblastic anemia, mild deficiency may be associated with neurocognitive and other consequences. B₁₂ deficiency is best diagnosed using a combination of tests because none alone is completely reliable. The features of B₁₂ deficiency are variable and may be atypical. Timely diagnosis is important, and treatment is gratifying. Failure to diagnose B₁₂ deficiency can have dire consequences, usually neurological. This review is written from the perspective of a practicing hematologist.

Vitamin B12 and Homocysteine Associations with Gait Speed in Older Adults: The Baltimore Longitudinal Study of Aging

OBJECTIVES

This study aimed to assess the independent associations of serum levels of vitamin B12 and plasma concentrations of homocysteine with gait speed decline.

DESIGN, SETTING, PARTICIPANTS

This study utilized longitudinal analysis of participants 50 years or older from The Baltimore Longitudinal Study of Aging, N=774.

MEASUREMENTS

Gait speed (m/s) was assessed using the 6-meter usual pace test. Vitamin B12 and homocysteine concentrations were collected using standard clinical protocols. Linear mixed effects regression was stratified by baseline age category (50-69, 70-79, and ≥80 years old).

RESULTS

Mean follow-up time for the total study sample was 5.4 ± 2.0 years. No association between vitamin B12 and gait speed decline over the follow-up time for any age group was found. Elevated homocysteine concentrations were associated with decline in gait speed after adjustment for covariates (50-69: β= -0.005, p=.057; 70-79: β= -0.013, p<.001, ≥80: β= -0.007, p=.054).

CONCLUSION

Homocysteine and vitamin B12 are inversely related, yet only homocysteine was associated with gait speed decline in this population of healthy older adults. Given these results, future research should be directed towards investigating the relationship in populations with greater variation in vitamin B12 concentrations and other mechanisms influencing homocysteine concentrations.

Causes, Consequences and Public Health Implications of Low B-Vitamin Status in Ageing

The potential protective roles of folate and the metabolically related B-vitamins (vitamins B12, B6 and riboflavin) in diseases of ageing are of increasing research interest. The most common cause of folate and riboflavin deficiencies in older people is low dietary intake, whereas low B12 status is primarily associated with food-bound malabsorption, while sub-optimal vitamin B6 status is attributed to increased requirements in ageing. Observational evidence links low status of folate and the related B-vitamins (and/or elevated concentrations of homocysteine) with a higher risk of degenerative diseases including cardiovascular disease (CVD), cognitive dysfunction and osteoporosis. Deficient or low status of these B-vitamins alone or in combination with genetic polymorphisms, including the common MTHFR 677 C → T polymorphism, could contribute to greater disease risk in ageing by causing perturbations in one carbon metabolism. Moreover, interventions with the relevant B-vitamins to optimise status may have beneficial effects in preventing degenerative diseases. The precise mechanisms are unknown but many have been proposed involving the role of folate and the related B-vitamins as co-factors for one-carbon transfer reactions, which are fundamental for DNA and RNA biosynthesis and the maintenance of methylation reactions. This review will examine the evidence linking folate and related B-vitamins with health and disease in ageing, associated mechanisms and public health implications.

Holotranscobalamin (HoloTC, Active-B12) and Herbert's model for the development of vitamin B12 deficiency: a review and alternative hypothesis

The concentration of total vitamin B12 in serum is not a sufficiently sensitive or specific indicator for the reliable diagnosis of vitamin B12 deficiency. Victor Herbert proposed a model for the staged development of vitamin B12 deficiency, in which holotranscobalamin (HoloTC) is the first indicator of deficiency. Based on this model, a commercial immunoassay has been controversially promoted as a replacement for the total vitamin B12 test. HoloTC is cobalamin (vitamin B12) attached to the transport protein transcobalamin, in the serum, for delivery to cells for metabolism. Although there have been many published reports supporting the claims for HoloTC, the results of some studies were inconsistent with the claim of HoloTC as the most sensitive marker of vitamin B12 deficiency. This review examines the evidence for and against the use of HoloTC, and concludes that the HoloTC immunoassay cannot be used to measure vitamin B12 status any more reliably than total vitamin B12, or to predict the onset of a metabolic deficiency, because it is based on an erroneous hypothesis and a flawed model for the staged development of vitamin B12 deficiency. The author proposes an alternative model for the development of vitamin B12 deficiency.

Laboratory assessment of vitamin B12 status

The detection and correction of vitamin B₁₂ (B₁₂) deficiency prevents megaloblastic anaemia and potentially irreversible neuropathy and neuropsychiatric changes. B₁₂ status is commonly estimated using the abundance of the vitamin in serum, with ∼148 pmol/L (200 ng/L) typically set as the threshold for diagnosing deficiency. Serum B₁₂ assays measure the sum of haptocorrin-bound and transcobalamin-bound (known as holotranscobalamin) B₁₂ It is only holotranscobalamin that is taken up by cells to meet metabolic demand. Although receiver operator characteristic curves show holotranscobalamin measurement to be a moderately more reliable marker of B₁₂ status than serum B₁₂, both assays have an indeterminate range. Biochemical evidence of metabolic abnormalities consistent with B₁₂ insufficiency is frequently detected despite an apparently sufficient abundance of the vitamin. Laboratory B₁₂ status markers that reflect cellular utilisation rather than abundance are available. Two forms of B₁₂ act as coenzymes for two different reactions. Methionine synthase requires methylcobalamin for the remethylation of methionine from homocysteine. A homocysteine concentration >20 µmol/L may suggest B₁₂ deficiency in folate-replete patients. In the second B₁₂-dependent reaction, methylmalonyl-CoA mutase uses adenosylcobalamin to convert methylmalonyl-CoA to succinyl-CoA. In B₁₂ deficiency excess methylmalonyl-CoA is hydrolysed to methylmalonic acid. A serum concentration >280 nmol/L may suggest suboptimal status in young patients with normal renal function. No single laboratory marker is suitable for the assessment of B₁₂ status in all patients. Sequential assay selection algorithms or the combination of multiple markers into a single diagnostic indicator are both approaches that can be used to mitigate inherent limitations of each marker when used independently.

Methylmalonic acid and neutrophil morphometric index in laboratory diagnosis of cobalamin deficiency without macrocytosis

INTRODUCTION

This study aimed to investigate the utility of methylmalonic acid (MMA) and neutrophil Cell Population Data, available on the Beckman Coulter LH750 Analyser (Miami, FL, USA), in laboratory assessment of cobalamin status in patients at risk of cobalamin deficiency, without macrocytosis and inflammation.

METHODS

The study group included 189 patients. Neutrophil Cell Population Data along with vitamin B12 and homocysteine were assessed in regard to MMA tertile groups.

RESULTS

Statistically significant differences were between lower and upper MMA tertile in serum B12 (P ˂ 0.001), homocysteine (P = 0.001) and neutrophil morphometric index, NeS-DW (P = 0.029). Also, serum B12 concentrations were significantly different between lower and middle MMA tertile, P = 0.005. Receiver operating characteristic analysis of NeS-DW ability to detect MMA˃367 nmol/L revealed a significant area under the curve AUC = 0.761 P ˂ 0.001 95% CI 0.693-0.830. Optimal cut-off value was NeS-DW˃3.51% with sensitivity of 74.19% and specificity of 68.87%.

CONCLUSION

In patients at risk of cobalamin deficiency and normal MCV, classification according to MMA revealed cobalamin status differences. Neutrophil morphometric index may be an indicator of early changes in neutrophil nucleus morphology caused by impaired cobalamin status.

Experimental vitamin B12 deficiency in a human subject: a longitudinal investigation of the performance of the holotranscobalamin (HoloTC, Active-B12) immunoassay

Based on Victor Herbert’s model for sequential stages in the development of vitamin B₁₂ deficiency, the holotranscobalamin (HoloTC) immunoassay has controversially been promoted as a more specific and sensitive replacement for the total vitamin B₁₂ test, for the diagnosis of deficiency. There have been no longitudinal studies, by means of experimental cobalamin deficiency, because ethical considerations prevent such risky studies on patients or healthy human volunteers. The objective was to provide a detailed record of the response of HoloTC, compared to total vitamin B₁₂ and metabolites, to the development of experimental vitamin B₁₂ deficiency in an initially replete human subject. This 54 year old male, with a vitamin B₁₂ deficiency possibly caused by a defect in the intracellular cobalamin metabolism, ensured an initially replete condition by means of oral doses of cyanocobalamin supplements at 1000 μg/day for 12 weeks. The subject then depleted himself of vitamin B₁₂, by withholding treatment and using a low-cobalamin diet, until significant metabolic disturbances were observed. The responses of serum total vitamin B₁₂ and HoloTC and the two metabolites, plasma methylmalonic acid and homocysteine, were monitored by weekly blood tests. HoloTC was not significantly more sensitive than either total serum vitamin B₁₂ or total homocysteine, and was much less sensitive than methylmalonic acid. HoloTC decreased from an initial concentration of >128 pmol/L to a minimum of 33 pmol/L on day 742, the only day on which it fell below the lower limit of the reference interval. Total vitamin B₁₂ decreased from an initial concentration of 606 pmol/L to a minimum of 171 pmol/L on day 728. Total homocysteine increased from an initial concentration of 8.4 μmol/L to a maximum of 14.2 μmol/L on day 609. Methylmalonic acid unexpectedly contained four distinct peaks; initially at 0.17 μmol/L, it first exceeded the upper limit of the reference interval on day 386, finally reaching a maximum peak of 0.90 μmol/L on day 658. The results of this experiment are inconsistent with Herbert’s hypothesis that HoloTC is the earliest marker of vitamin B₁₂ deficiency, and therefore do not support his model for the staged development of vitamin B₁₂ deficiency.

Prevalence and Risk Factors for Functional Vitamin B12 Deficiency in Patients with Crohn's Disease

BACKGROUND

Crohn's disease (CD) is a risk factor for vitamin B12 deficiency due to frequent involvement of the terminal ileum. Conventional screening for B12 deficiency with serum B12 is relatively insensitive and measures total B12 concentration, of which a minority is present in a biologically active form. Holotranscobalamin (holoTC) combined with methylmalonic acid (MMA) is believed to be more accurate in identifying impaired B12 status. We evaluated the prevalence and risk factors for B12 deficiency using holoTC supported by MMA among patients with CD.

METHODS

We performed a single-center service evaluation of 381 patients with CD who underwent B12 assessment (holoTC/MMA) and compared them with 141 patients with ulcerative colitis. Eighty-nine patients with CD underwent paired serum B12 and holoTC. Among patients with CD, risk factors including terminal ileal resection length, ileal inflammation on endoscopy, and disease characteristics on magnetic resonance imaging were recorded.

RESULTS

Prevalence of B12 deficiency among patients with CD was 33% compared with 16% in ulcerative colitis (P < 0.0001). In 89 patients who underwent paired tests, conventional testing identified B12 deficiency in 5% of patients with CD, which increased to 32% using holoTC/MMA. Independent risk factors for B12 deficiency were ileal resection length ≤20 cm (odds ratio: 3.0, 95% confidence interval, 1.5-6.0, P = 0.002) and >20 cm (odds ratio: 6.7, 95% confidence interval, 3.0-14.7, P < 0.0001) and ileal inflammation (odds ratio: 3.9, 95% confidence interval, 2.2-6.9, P < 0.0001). On magnetic resonance imaging, active terminal ileal inflammation (P = 0.02) and an increased disease burden (≥1 skip lesion, P = 0.01 and prestenotic dilatation >3 cm, P = 0.01) were associated with B12 deficiency.

CONCLUSIONS

Vitamin B12 deficiency is common in patients with CD. holoTC supported by MMA identifies patients with B12 deficiency considered replete on conventional testing.

Nutritional Supplementation with Chlorella pyrenoidosa Lowers Serum Methylmalonic Acid in Vegans and Vegetarians with a Suspected Vitamin B₁₂ Deficiency

Since vitamin B12 occurs in substantial amounts only in foods derived from animals, vegetarians and particularly vegans are at risk of developing deficiencies of this essential vitamin. The chlorella used for this study is a commercially available whole-food supplement, which is believed to contain the physiologically active form of the vitamin. This exploratory open-label study was performed to determine if adding 9 g of Chlorella pyrenoidosa daily could help mitigate a vitamin B12 deficiency in vegetarians and vegans. Seventeen vegan or vegetarian adults (26-57 years of age) with a known vitamin B12 deficiency, as evidenced by a baseline serum methylmalonic acid (MMA) level above 270 nmol/L at screening, but who otherwise appeared healthy were enrolled in the study. Each participant added 9 g of C. pyrenoidosa to their daily diet for 60 ± 5 days and their serum MMA, vitamin B12, homocysteine (Hcy) levels as well as mean corpuscular volume (MCV), hemoglobin (Hgb), and hematocrit (Hct) were measured at 30 and 60 days from baseline. After 30 and 60 days, the serum MMA level fell significantly (P < .05) by an average ∼34%. Fifteen of the 17 (88%) subjects showed at least a 10% drop in MMA. At the same time, Hcy trended downward and serum vitamin B12 trended upward, while MCV, Hgb, and Hct appeared unchanged. The results of this work suggest that the vitamin B12 in chlorella is bioavailable and such dietary supplementation is a natural way for vegetarians and vegans to get the vitamin B12 they need.

Methylmalonic acid quantified in dried blood spots provides a precise, valid, and stable measure of functional vitamin B-12 status in healthy women

Methylmalonic acid (MMA) is a sensitive and specific functional biomarker of vitamin B-12 status, commonly assessed in plasma or serum. Dried blood spots (DBSs) allow simpler and more cost-efficient blood sampling than plasma. To facilitate convenient testing for vitamin B-12 deficiency in large-scale surveys and in population groups from remote areas, we developed a method for MMA quantification in DBSs and tested its applicability as well as the long-term stability of MMA in DBSs at various temperatures. MMA was extracted from an 8-mm DBS punch with water:methanol (95:5, v:v) and methyl-d3-malonic acid as the internal standard. After sample cleanup by ultrafiltration and hexane extraction, MMA was quantified by using reversed-phase LC-tandem mass spectrometry. Extraction conditions were optimized to maximize the detection signal and achieve DBS extract concentrations above the lowest limit of quantification (signal-to-noise ratio ≥ 10) of 10 nmol/L. Recovery was between 93% and 96%. Intra- and interassay variation (CV%) for DBS MMA was 0.49% and 2.3%, respectively. Calibrators showed linearity (R(2) = 0.998) between 10 and 10,000 nmol/L. In 94 healthy women, MMA concentrations in DBS extract (min-max: 10.2-80.5 nmol/L) and plasma (min-max: 68-950 nmol/L) were correlated (ρ = 0.90) (P < 0.001). MMA concentrations in DBSs were stable at room temperature for 1 wk, in the refrigerator for 8 wk, and at -80°C for at least 1 y. This simple and robust method allows quantification of MMA in DBSs of healthy individuals. The linear relation between plasma and DBS MMA suggests that DBS MMA could predict plasma MMA, the current reference indicator for functional vitamin B-12 deficiency. With the advantages of minimally invasive specimen collection and no need for laborious blood processing steps, this method has the potential to be a reliable, convenient, and field-applicable alternative for assessment of vitamin B-12 status.

Vitamin B12 deficiency in inflammatory bowel disease: prevalence, risk factors, evaluation, and management

BACKGROUND

Management of vitamin B(12) (cobalamin, Cbl) deficiency in inflammatory bowel disease (IBD) is often not evidenced-based because of uncertainty on whether it causes enough malabsorption to result in clinical disease. This systematic review examines whether IBD predisposes to Cbl deficiency. We provide an approach to the management of abnormal Cbl values in IBD based on current literature and consensus-based guidelines.

METHODS

An extensive search of the Ovid MEDLINE and EMBASE databases by independent reviewers identified 42 articles with a total of 3732 patients evaluating Cbl deficiency in IBD.

RESULTS

Crohn's disease without ileal resection, regardless of disease location in the ileum, did not increase the risk for Cbl deficiency. Ileal resections greater than 30 cm were associated with Cbl deficiency in Crohn's disease, whereas those less than 20 cm were not. The effects of 20 to 30 cm resections were inconsistent. Ulcerative colitis did not predispose to deficiency. All studies failed to use confirmatory biomarker testing as stipulated by diagnostic guidelines for Cbl deficiency.

CONCLUSIONS

This literature does not support an association of Crohn's disease in general, regardless of ileal involvement, with Cbl deficiency. Only ileal resections greater than 20 cm in Crohn's disease predispose to deficiency and warrant treatment. Based on these findings, we suggest a diagnostic and therapeutic algorithm. All findings and recommendations require verification in further studies using confirmatory biomarkers as per diagnostic guidelines for Cbl deficiency. Serum Cbl levels alone are likely insufficient to diagnose deficiency in asymptomatic patients.

Prevalence of vitamin B(12) depletion and deficiency in Liechtenstein

OBJECTIVE

Data about vitamin B(12) (B(12)) deficiency in the general population are scarce. The present study was performed to determine the prevalence of B(12) deficiency in the general population of the Principality of Liechtenstein, as well as to identify sub-populations potentially at high risk.

DESIGN

Retrospective study.

SETTING

Ambulatory setting, population of the Principality of Liechtenstein.

SUBJECTS

Seven thousand four hundred and twenty-four patients seeking medical attention whose serum samples were referred for routine work-up in an ambulatory setting were consecutively enrolled. Serum total B(12) was determined in all patients in this cohort. In addition, for a subgroup of 1328 patients, serum holotranscobalamin was also measured. Prevalence of B(12) deficiency was calculated. Further, multivariate logistical regression models were applied to identify covariates independently associated with B(12) deficiency and depletion.

RESULTS

Nearly 8% of the general population was suffering from either B(12) depletion or deficiency. The ratio between B(12) depletion and deficiency was 2:1 for all age ranges. Pathological changes were detected predominantly in older people. Female gender was a significant predictor of B(12) depletion. In the cohort, nearly 40% exhibited either depletion or deficiency of B(12).

CONCLUSIONS

B(12) depletion and deficiency are common in Liechtenstein, a Central European country. The measurement of biochemical markers represents a cost-efficient and valid assessment of the B(12) state. When a deficiency of B(12) is diagnosed at an early stage, many cases can be treated or prevented, with beneficial effects on individual outcomes and subsequent potential reductions in health-care costs.

Neurologic aspects of cobalamin (B12) deficiency

Optimal functioning of the central and peripheral nervous system is dependent on a constant supply of appropriate nutrients. Particularly important for optimal functioning of the nervous system is cobalamin (vitamin B12). Cobalamin deficiency is particularly common in the elderly and after gastric surgery. Many patients with clinically expressed cobalamin deficiency have intrinsic factor-related malabsorption such as that seen in pernicious anemia. The commonly recognized neurological manifestations of cobalamin deficiency include a myelopathy with or without an associated neuropathy. This review deals with neurological aspects of vitamin B12 deficiency and attempts to highlight recent developments.

Interactions between plasma concentrations of folate and markers of vitamin B(12) status with cognitive performance in elderly people not exposed to folic acid fortification: the Hordaland Health Study

A combination of high folate with low vitamin B12 plasma status has been associated with cognitive impairment in a population exposed to mandatory folic acid fortification. The objective of the present study was to examine the interactions between plasma concentrations of folate and vitamin B12 markers in relation to cognitive performance in Norwegian elderly who were unexposed to mandatory or voluntary folic acid fortification. Cognitive performance was assessed by six cognitive tests in 2203 individuals aged 72-74 years. A combined score was calculated using principal component analysis. The associations of folate concentrations, vitamin B12 markers (total vitamin B12, holotranscobalamin (holoTC) and methylmalonic acid (MMA)) and their interactions in relation to cognitive performance were evaluated by quantile regression and least-squares regression, adjusted for sex, education, apo-ɛ4 genotype, history of CVD/hypertension and creatinine. Cross-sectional analyses revealed an interaction (P= 0·009) between plasma concentrations of folate and vitamin B12 in relation to cognitive performance. Plasma vitamin B12 concentrations in the lowest quartile ( < 274 pmol/l) combined with plasma folate concentrations in the highest quartile (>18·5 nmol/l) were associated with a reduced risk of cognitive impairment compared with plasma concentrations in the middle quartiles of both vitamins (OR 0·22, 95 % CI 0·05, 0·92). The interaction between folate and holoTC or MMA in relation to cognitive performance was not significant. In conclusion, this large study population unexposed to mandatory folic acid fortification showed that plasma folate, but not plasma vitamin B12, was associated with cognitive performance. Among the elderly participants with vitamin B12 concentrations in the lower range, the association between plasma folate and cognitive performance was strongest.

Role of serum holotranscobalamin (holoTC) in the diagnosis of patients with low serum cobalamin. Comparison with methylmalonic acid and homocysteine

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.

Holotranscobalamin is not influenced by decreased renal function in elderly men: the MrOS Sweden study

BACKGROUND

Subclinical cobalamin deficiency is common in the elderly, but the sensitivity and specificity of serum total cobalamin for this diagnosis is poor. Serum holotranscobalamin (holoTC), a measure of biologically available cobalamin, is considered a better marker for early cobalamin depletion than total cobalamin. However, in elderly populations, health-related reference intervals for holoTC and correlations to renal function are not entirely clear.

METHODS

HoloTC was determined with an automated microparticle enzyme immunoassay (AxSYM®) in 790 elderly non-vitamin-supplemented Swedish men, median age 75.3 years. Renal function was assessed with creatinine, cystatin C and estimated glomerular filtration rate (eGFR calculated from creatinine).

RESULTS

Median holoTC was 51.8 pmol/L, the health-related reference interval 19.6-132.3 pmol/L. There was no significant difference in mean holoTC in probands with normal compared to high creatinine (P = 0.80) and cystatin C (P = 0.82). No significant differences between the quartiles of creatinine or cystatin C in mean of log holoTC were seen. HoloTC correlated strongly with total cobalamin (r = 0.69, P < 0.001), weaker with eGFRcreatinine (r = -0.09, P < 0.05) and creatinine (r = 0.09, P < 0.05), the latter correlation was only seen in subjects with creatinine <100 µmol/L. HoloTC correlated negatively with plasma total homocysteine (r = -0.24, P < 0.001), but not with cystatin C and age.

CONCLUSIONS

Serum holoTC in healthy elderly men shows the same distribution as earlier described for a younger reference population. In this group of elderly subjects, holoTC did not correlate to reduced renal function. Thus, holoTC appears to be a promising tool for evaluating cobalamin status also in elderly populations.

Advanced age as a risk factor for folate-associated functional cobalamin deficiency

OBJECTIVES

To determine whether high serum folate levels contribute to metabolite changes in elderly subjects with normal cobalamin levels.

DESIGN

Case series.

SETTING

Outpatient clinic at a university-based staff model health maintenance organization.

PARTICIPANTS

Two hundred thirty-three ambulatory individuals without diabetes mellitus with normal renal function and normal cobalamin levels evaluated for cobalamin deficiency.

MEASUREMENTS

Cobalamin, serum folate, methylmalonic acid (MMA), and homocysteine.

RESULTS

Older individuals (≥60) with low-normal cobalamin levels (201-300 pg/mL) had higher MMA and lower homocysteine levels when serum folate levels were high (>20 ng/mL) than when serum folate levels were normal (P < .02), but serum folate levels within the normal range were not a determinant of either metabolite. In younger subjects with low-normal cobalamin levels, high serum folate levels were not associated with significant differences in either metabolite. At mid-normal cobalamin levels (301-600 pg/mL), high serum folate levels were associated with lower homocysteine levels in older adults (P < .001) but not with differences in MMA in either age group. Cobalamin therapy decreased or normalized MMA and homocysteine in 89% or more of participants even at pretherapy cobalamin levels greater than 600 pg/mL.

CONCLUSION

High serum folate levels are associated with higher MMA levels when cobalamin levels are low-normal, and this effect is age dependent, not progressive within the normal serum folate range (suggesting a threshold effect), and reversed by cobalamin therapy. Because MMA may be neurotoxic, these findings suggest caution in the use of folic acid supplements in elderly adults.

Diagnosis and management of clinical and subclinical cobalamin deficiencies: why controversies persist in the age of sensitive metabolic testing

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.

An observational study of the effect of metformin on B12 status and peripheral neuropathy

Aims

Metformin is associated with lowering of vitamin B12 levels. We hypothesise that holotranscobalamin (holoTC) and methylmalonic acid (MMA) are more sensitive indicators of B12 deficiency in patients receiving metformin therapy, and that these correlate with declining peripheral neurological function.

Methods

Patients with type 2 diabetes were recruited and divided into those receiving metformin for greater than 6 months and a non-metformin group. Baseline characteristics were measured in both groups including vitamin B12, holoTC and MMA concentrations. Neurological function was assessed using neurothesiometry, monofilament, Neuropathy Total Symptom Score-6 questionnaire and the Self-administered Leeds Assessment of Neuropathic Symptoms and Signs questionnaire.

Results

In total, 202 patients were recruited: 152 in the metformin group and 50 in the non-metformin group. Vitamin B12 levels were lower in the metformin group (219.1±105.4 ng/L, 281.4±95.1 ng/L, p<0.001). HoloTC was significantly lower in the metformin group (54.8±30.5 pmol/L, 70.1±26.0 pmol/L, p=0.002). No significant difference in serum MMA was observed between the two groups (0.40±0.26 μmol/L, 0.35±0.22, p=0.23). No significant difference in neurological function was observed between the groups.

Conclusion

Although metformin therapy is associated with lower vitamin B12 status there does not appear to be any significant effect on peripheral neuropathy in those receiving metformin. We do not recommend changing current practice to routinely monitor or replace patients receiving metformin with vitamin B12 unless clinically indicated.

Screening for metabolic vitamin B12 deficiency by holotranscobalamin in patients suspected of vitamin B12 deficiency: a multicentre study

BACKGROUND

Vitamin B(12) deficiency occurs frequently, especially among the elderly. However, screening for vitamin B(12) deficiency is hampered by poor sensitivity of the existing total vitamin B(12) assay. Methylmalonic acid (MMA) is considered as the most representative indicator of metabolic vitamin B(12) deficiency and is used as such in this study. The aim of this study was to validate the clinical usefulness of holotranscobalamin (holoTC) as an initial screening assay for metabolic vitamin B(12) deficiency in a mixed patient population.

METHODS

Three hundred and sixty blood samples were collected by five Dutch hospitals. Vitamin B(12) and holoTC in serum were measured (AxSYM; Abbott). MMA in serum was measured by tandem mass spectrometry (LC-MS/MS).

RESULTS

Receiver operating curve (ROC) analysis demonstrated a greater area under the curve (AUC) for holoTC than for vitamin B(12) in detecting vitamin B(12) deficiency characterized by three predefined cut-off levels of MMA. A cut-off value of 32 pmol/L of holoTC resulted in the highest sensitivity (83%) with acceptable specificity (60%) in detecting MMA concentrations above 0.45 μmol/L. The combination of vitamin B(12) and holoTC did not improve diagnostic accuracy at this cut-off level.

CONCLUSIONS

HoloTC has a better diagnostic accuracy than vitamin B(12) and can replace the existing vitamin B(12) assay as a primary screening test in patients suspected of vitamin B(12) deficiency. Critical evaluation of cut-off values of holoTC indicated that a cut-off value of 32 pmol/L can be considered in screening for metabolic vitamin B(12) deficiency (defined by MMA > 0.45μmol/L) in a mixed patient population.

Holotranscobalamin, a marker of vitamin B-12 status: analytical aspects and clinical utility

Approximately one-quarter of circulating cobalamin (vitamin B-12) binds to transcobalamin (holoTC) and is thereby available for the cells of the body. For this reason, holoTC is also referred to as active vitamin B-12. HoloTC was suggested as an optimal marker of early vitamin B-12 deficiency >20 y ago. This suggestion led to the development of suitable assays for measurement of the compound and clinical studies that aimed to show the benefit of measurement of holoTC rather than of vitamin B-12. Today holoTC can be analyzed by 3 methods: direct measurement of the complex between transcobalamin and vitamin B-12, measurement of vitamin B-12 attached to transcobalamin, or measurement of the amount of transcobalamin saturated with vitamin B-12. These 3 methods give similar results, but direct measurement of holoTC complex is preferable in the clinical setting from a practical point of view. HoloTC measurement has proven useful for the identification of the few patients who suffer from transcobalamin deficiency. In addition, holoTC is part of the CobaSorb test and therefore useful for assessment of vitamin B-12 absorption. Clinical studies that compare the ability of holoTC and vitamin B-12 to identify individuals with vitamin B-12 deficiency (elevated concentration of methylmalonic acid) suggest that holoTC performs better than total vitamin B-12. To date, holoTC has not been used for population-based assessments of vitamin B-12 status, but we suggest that holoTC is a better marker than total vitamin B-12 for such studies.

Biomarkers of vitamin B-12 status in NHANES: a roundtable summary

A roundtable to discuss the measurement of vitamin B-12 (cobalamin) status biomarkers in NHANES took place in July 2010. NHANES stopped measuring vitamin B-12-related biomarkers after 2006. The roundtable reviewed 3 biomarkers of vitamin B-12 status used in past NHANES--serum vitamin B-12, methylmalonic acid (MMA), and total homocysteine (tHcy)--and discussed the potential utility of measuring holotranscobalamin (holoTC) for future NHANES. The roundtable focused on public health considerations and the quality of the measurement procedures and reference methods and materials that past NHANES used or that are available for future NHANES. Roundtable members supported reinstating vitamin B-12 status measures in NHANES. They noted evolving concerns and uncertainties regarding whether subclinical (mild, asymptomatic) vitamin B-12 deficiency is a public health concern. They identified the need for evidence from clinical trials to address causal relations between subclinical vitamin B-12 deficiency and adverse health outcomes as well as appropriate cutoffs for interpreting vitamin B-12-related biomarkers. They agreed that problems with sensitivity and specificity of individual biomarkers underscore the need for including at least one biomarker of circulating vitamin B-12 (serum vitamin B-12 or holoTC) and one functional biomarker (MMA or tHcy) in NHANES. The inclusion of both serum vitamin B-12 and plasma MMA, which have been associated with cognitive dysfunction and anemia in NHANES and in other population-based studies, was preferable to provide continuity with past NHANES. Reliable measurement procedures are available, and National Institute of Standards and Technology reference materials are available or in development for serum vitamin B-12 and MMA.

Biomarkers of cobalamin (vitamin B-12) status in the epidemiologic setting: a critical overview of context, applications, and performance characteristics of cobalamin, methylmalonic acid, and holotranscobalamin II

Cobalamin deficiency is relatively common, but the great majority of cases in epidemiologic surveys have subclinical cobalamin deficiency (SCCD), not classical clinical deficiency. Because SCCD has no known clinical expression, its diagnosis depends solely on biochemical biomarkers, whose optimal application becomes crucial yet remains unsettled. This review critically examines the current diagnostic concepts, tools, and interpretations. Their exploration begins with understanding that SCCD differs from clinical deficiency not just in degree of deficiency but in fundamental pathophysiology, causes, likelihood and rate of progression, and known health risks (the causation of which by SCCD awaits proof by randomized clinical trials). Conclusions from SCCD data, therefore, often may not apply to clinical deficiency and vice versa. Although many investigators view cobalamin testing as unreliable, cobalamin, like all diagnostic biomarkers, performs satisfactorily in clinical deficiency but less well in SCCD. The lack of a diagnostic gold standard limits the ability to weigh the performance characteristics of metabolic biomarkers such as methylmalonic acid (MMA) and holotranscobalamin II, whose specificities remain incompletely defined outside their relations to each other. Variable cutoff selections affect diagnostic conclusions heavily and need to be much better rationalized. The maximization of reliability and specificity of diagnosis is far more important today than the identification of ever-earlier stages of SCCD. The limitations of all current biomarkers make the combination of ≥2 test result abnormalities, such as cobalamin and MMA, the most reliable approach to diagnosing deficiency in the research setting; reliance on one test alone courts frequent misdiagnosis. Much work remains to be done.

Diagnostic accuracy of holotranscobalamin, methylmalonic acid, serum cobalamin, and other indicators of tissue vitamin B₁₂ status in the elderly

BACKGROUND

Vitamin B₁₂ deficiency is common among the elderly, and early detection is clinically important. However, clinical signs and symptoms have limited diagnostic accuracy and there is no accepted reference test method.

METHODS

In elderly subjects (n = 700; age range 63-97 years), we investigated the ability of serum cobalamin, holotranscobalamin (holoTC), total homocysteine (tHcy), methylmalonic acid (MMA), serum and erythrocyte folate, and other hematologic variables to discriminate cobalamin deficiency, defined as red blood cell cobalamin <33 pmol/L.

RESULTS

Serum holoTC was the best predictor, with area under the ROC curve (95% CI) 0.90 (0.86-0.93), and this was significantly better (P ≤ 0.0002) than the next best predictors; serum cobalamin, 0.80 (0.75-0.85), and MMA, 0.78 (0.72-0.83). For these 3 analytes, we constructed a 3-zone partition of positive and negative zones and a deliberate indeterminate zone between. The boundaries were values of each test that resulted in a posttest probability of deficiency of 60% and a posttest probability of no deficiency of 98%. The proportion of indeterminate observations for holoTC, cobalamin, and MMA was 14%, 45%, and 50%, respectively. Within the holoTC indeterminate zone (defined as 20-30 pmol/L), discriminant analysis selected only erythrocyte folate, which correctly allocated 65% (58/89) of the observations. Renal dysfunction compromised the diagnostic accuracy of MMA but not holoTC or serum cobalamin.

CONCLUSIONS

This study supports the use of holoTC as the first-line diagnostic procedure for vitamin B₁₂ status.