Immune complexes and persistent high levels of serum vitamin B12

Homocysteine-a retrospective and prospective appraisal

The biologically important amino acid homocysteine links sulfur, methionine, and one-carbon metabolism. This review describes its initial discovery, the identification of the clinical condition of "homocystinuria" and the recognition of its close relationship to folate and vitamin B12 metabolism. It discusses the history behind its current association with diverse diseases including neural tube defects, cardio- and cerebrovascular disease and, more recently, dementia and Alzheimer's Disease. It also explores current controversies and considers potential future research directions. It is intended to give a general overview of homocysteine in relation to health and disease.

FUNCTIONAL VITAMIN B12 DEFICIENCY: IMPROVING METHYLMALONIC ACID REFERENCE INTERVALS IN URINE

BACKGROUND

AIM Most laboratory requests focus on the detection of possible vitamin B12 deficiency. In this context, methylmalonic acid (MMA) is reported as the best biomarker. The aim of our study was to establish the biological reference interval for MMA in urine, and assess the influence of age, sex, and vitamin B12 status on MMA concentrations.

METHODS

This is a prospective observational study considering individuals with normal results for blood count and liver and kidney function. Individuals who presented supplementation, any pathology or treatment that could cause cobalamin metabolism disorders, and pregnant women were excluded. Likewise, individuals whose vitamin B12 result presented antibody-mediated interference were excluded. Individuals were grouped by age-group and sex. Reference intervals were determined by non-parametric calculation (percentiles 1-99).

RESULTS

It was established a single reference interval [0.52 (CI_90%: 0.50-0.54) - 5.75 (CI_90%: 5.57-6.17) mmolMMA/mol creatinine], with 100% of individuals with MMA above the upper limit of reference presenting a total vitamin B12 concentration ≤238pmol/L.

CONCLUSION

The establishment of optimal reference intervals for methylmalonic acid excretion in urine is crucial in individuals with a suspicion of functional vitamin B12 deficiency. However, the possibility of establishing a cut-off value for total vitamin B12 suggesting subclinical deficiency remains a challenge for this magnitude.

Challenges in the diagnosis of hypervitaminemia B12. Interference by immunocomplexes

BACKGROUND-AIM

High vitamin B12 concentrations are considered a common finding in clinical practice. Thanks to immunoassay accessibility, vitamin B12 has become a usual test in routine health checkups. However, these analytical methods usually present antibody-mediated interferences. Our aim was to propose an algorithm for the screening of antibody-mediated analytical interferences on vitamin B12 immunoassays on the Alinity platform.

METHODS

Observational, prospective, case-control study was performed during 12 months. Individuals with persistently elevated cobalamin concentrations [>554 pmol/L] were considered as cases in the absence of supplementation or other justifying cause. Individuals under treatment with vitamin B12, or in the context of alcoholism were included as controls. A thorough interference study by macromolecules in immunoassays was performed in serum samples: PEG precipitation, rheumatoid factor, heterophile antibodies and gel permeation chromatography (GPC). Albumin, total B12, IgG and IgM were measured in every GPC collected fraction and chromatograms were drafted.

RESULTS

Up to 45% of cases presented interference by B12-immunocomplexes and the precipitation for all of them was >50%. The individual with the lowest interfered vitamin B12 result was 661 pmol/L.

CONCLUSION

The presence of antibody-mediated interferences, mainly B12-immunocomplexes, is a relatively common phenomenon. A simple algorithm for the screening of interferences is useful and reliable in ruling out healthy individuals and highly cost-effective.

Age- and ethnicity-related reference intervals for serum vitamin B12

BACKGROUND

Age and ethnicity are known to influence serum vitamin B₁₂ (B₁₂) concentration, yet universal reference intervals (RIs) are typically applied by laboratories. Both lower and upper RI limits for B₁₂ are clinically relevant. Low values suggest deficiency leading to anemia and/or neurological impairment, while high values are not always an innocuous consequence of high B₁₂ intake but are associated with some cancers, autoimmune, liver, and renal diseases. This work aimed to establish age- and ethnicity-related RIs for B₁₂ using a modified indirect method based on Hoffmann's approach.

METHODS

A total of 72,091 anonymized B₁₂ results (Jan 2018-Nov 2019) were analyzed from an ethnically-diverse South-East London general practice patient population. Patients belonged to five ethnic groups: Asian, Black, White, Mixed, or Other. Multiple records for the same patient and results with missing ethnicity were excluded from the analysis of adult RIs. B₁₂ analyses were performed using ARCHITECT® (Abbott Diagnostics).

RESULTS

B₁₂ was significantly higher in Black compared with Asian and White adults. There were no differences in B₁₂ between Asian and White adults. Children (all ethnicities) between 2 and 5 years old had the highest B₁₂. Because of the small number of children (up to the age of 13) in each ethnic-related age category, all ethnic groups were combined to obtain age-related RIs. The children's RIs ranged from 159 to 1025 pmol/L for 0-1-year-olds to 276-1102 pmol/L for 2-5-year-olds. The RIs for Black and White/Asian people >13 years of age were 166-805 pmol/L and 134-511 pmol/L respectively.

CONCLUSIONS

The application of age- and ethnicity-appropriate RIs into diagnostic practice will provide a more accurate evaluation of B₁₂ status when using the B₁₂ test alone or in combination with other markers.

"Macro transcobalamin causing raised vitamin B12: Case-based laboratory investigation"

Determination of plasma vitamin B12 (B12) is a frequently requested laboratory analysis, mainly employed to establish B12 deficiency. However, an increased level of B12 is a common unexpected finding that may be related to an increased concentration of one of the B12 binding proteins, haptocorrin or transcobalamin. This paper describes the extensive laboratory evaluation of a patient with an elevated level of plasma B12 with various well-established assays. Initial studies suggested the presence of a macromolecule consisting of haptocorrin bound B12. Specific determinations of the B12-binding proteins revealed normal amounts of haptocorrin but a markedly increase in both total and B12 saturated transcobalamin (holo-TC). The results are in accord with the presence of macro-transcobalamin. These experiments reveal that determination of the nature of the B12-macromolecules is troublesome due to differences in assays applied to measure these proteins. In addition, this publication creates awareness of macro-holo-TC as a cause of an unexplained increased B12 level.

Macro-B12 masking B12 deficiency

In clinical practice, the finding of an elevated serum B₁₂ concentration is often the consequence of supplementation with B₁₂ in either oral form or injections. Also, elevated serum B₁₂ may be associated with underlying disorders, like liver diseases or a (haematologic) malignancy. Only a few studies have shown that it may also be the consequence of complex formation of B₁₂-vitamin binding proteins with immunoglobulins, the so-called macro-B₁₂. We describe a young woman who previously was diagnosed with B₁₂ deficiency, and in whom, after cessation of B₁₂ injection treatment, neurologic symptoms re-appeared, and despite this, repeatedly elevated serum B₁₂ concentrations above the upper limit of the assay were found. We demonstrated that this was caused by the presence of macro-B₁₂, which not only resulted in erroneous and longstanding elevated serum B₁₂, but also masked her underlying B₁₂ deficiency.

Vitamin B12 status in health and disease: a critical review. Diagnosis of deficiency and insufficiency - clinical and laboratory pitfalls

Vitamin B₁₂ (cobalamin) is an essential cofactor for two metabolic pathways. It is obtained principally from food of animal origin. Cobalamin becomes bioavailable through a series of steps pertaining to its release from dietary protein, intrinsic factor-mediated absorption, haptocorrin or transcobalamin-mediated transport, cellular uptake, and two enzymatic conversions (via methionine synthase and methylmalonyl-CoA-mutase) into cofactor forms: methylcobalamin and adenosylcobalamin. Vitamin B₁₂ deficiency can masquerade as a multitude of illnesses, presenting different perspectives from the point of view of the hematologist, neurologist, gastroenterologist, general physician, or dietician. Increased physician vigilance and heightened patient awareness often account for its early presentation, and testing sometimes occurs during a phase of vitamin B₁₂ insufficiency before the main onset of the disease. The chosen test often depends on its availability rather than on the diagnostic performance and sensitivity to irrelevant factors interfering with vitamin B₁₂ markers. Although serum B₁₂ is still the most commonly used and widely available test, diagnostics by holotranscobalamin, serum methylmalonic acid, and plasma homocysteine measurements have grown in the last several years in routine practice. The lack of a robust absorption test, coupled with compromised sensitivity and specificity of other tests (intrinsic factor and gastric parietal cell antibodies), hinders determination of the cause for depleted B₁₂ status. This can lead to incorrect supplementation regimes and uncertainty regarding later treatment. This review discusses currently available knowledge on vitamin B₁₂, informs the reader about the pitfalls of tests for assessing its deficiency, reviews B₁₂ status in various populations at different disease stages, and provides recommendations for interpretation, treatment, and associated risks. Future directions for diagnostics of B₁₂ status and health interventions are also discussed.

Relationship between serum B12 concentrations and mortality: experience in NHANES

BACKGROUND

There is conflicting evidence in the literature on the association between (elevated) serum B12 concentrations and subsequent disease or mortality. We evaluated in the NHANES general population the association of serum B12 concentrations as well as vitamin B12 supplement intake with all-cause, cardiovascular, and cancer-related mortality, while taking into account demographic and lifestyle factors and significant other diseases which are known to be associated with poorer outcome.

METHODS

The main outcomes of our study were all-cause mortality, cardiovascular mortality, and cancer-related mortality. Mortality status and cause of death were determined by NHANES-linked National Death Index public access files through December 31, 2015. The association of serum B12 concentrations and vitamin B12 supplement intake with mortality was assessed with Cox proportional hazard (PH) models, with adjustment for a number of relevant demographic and lifestyle factors and comorbidity.

RESULTS

The final study population of 24,262 participants had a mean age of 48 (SD 19) years; 50.1% were males. The median follow-up duration was 109 months (range 1-201 months). On the census day of December 31, 2015, 3023 participants were determined as deceased (12.5%). The fully adjusted Cox PH model indicated that low serum B12 concentrations < 140 pmol/l were associated with a small increase in all-cause (hazard ratio, HR 1.39, 95% CI 1.08-1.78, p = 0.011) and cardiovascular (HR 1.64, 95% CI 1.08-2.47, p = 0.020) mortality. Similarly, high serum B12 concentrations > 700 pmol/l were associated with an increase in cardiovascular mortality only (HR 1.45, 95% CI 1.01-2.06, p = 0.042). Participants with a diagnosis of hypertension, dyslipidemia, CVD, and cancer more frequently used vitamin B12-containing supplements than those without these diagnoses. We could not demonstrate an association between vitamin B12 supplement intake and mortality, when adjusted for comorbidity.

CONCLUSIONS

In the general population of NHANES, low serum B12 concentrations were associated with a moderate increase in all-cause mortality. There was a small but significant increase in cardiovascular mortality in the groups with low or high serum B12. High intake of vitamin B12 in the form of supplements was not associated with any adverse effect on mortality and therefore can be regarded as safe.

Prevalence and clinical relevance of hypercobalaminaemia in dogs and cats

Hypocobalaminaemia is common in dogs and cats with exocrine pancreatic insufficiency and/or chronic enteropathy. While hypocobalaminaemia has been extensively studied, naturally-occurring serum hypercobalaminaemia (i.e. without supplementation) might be an underestimated finding in small animal medicine. Studies in human medicine have associated hypercobalaminaemia with neoplastic, hepatic and renal disease. Medical records of all dogs and cats with serum cobalamin concentration measurements (2007-2019) were retrospectively analysed; any that had received supplemental cobalamin were excluded from the analysis. Of 654 dogs, 3% (n = 21) were hypercobalaminaemic (median serum cobalamin concentration, 1307 ng/L [965 pmol/L]; range, 914-3561 ng/L [675-2628 pmol/L]). Chronic gastrointestinal signs were common in hypercobalaminaemic dogs (48%). Two of the 21 hypercobalaminaemic dogs were diagnosed with hypoadrenocorticism. Of 323 cats, 11% (n = 34) were hypercobalaminaemic (median serum cobalamin concentration, 1713 ng/L [1264 pmol/L]; range, 1370-3107 ng/L [1011-2293 pmol/L]). The following comorbidities were diagnosed in hypercobalaminaemic cats: chronic enteropathy, 65% (n = 22); acute or chronic pancreatitis, 24% (n = 8); cholangiohepatopathy, 18% (n = 6); gastric lymphoma, 6% (n = 2); and 3% hyperthyroidism (n = 1). Naturally-occurring increased serum cobalamin concentrations occurred infrequently in cats and even less often in dogs. Since hypercobalaminaemia can occur in dogs and cats with severe inflammatory, immune-mediated, and neoplastic conditions, it should not be ignored.

Elevated Plasma Vitamin B12 in Patients with Hepatic Glycogen Storage Diseases

Background: Hepatic glycogen storage diseases (GSDs) are inborn errors of metabolism affecting the synthesis or breakdown of glycogen in the liver. This study, for the first time, systematically assessed vitamin B₁₂ status in a large cohort of hepatic GSD patients. Methods: Plasma vitamin B₁₂, total plasma homocysteine (tHcy) and methylmalonic acid concentrations were measured in 44 patients with hepatic GSDs and compared to 42 healthy age- and gender-matched controls. Correlations of vitamin B₁₂ status with different disease markers of GSDs (including liver transaminase activities and triglycerides) as well as the vitamin B₁₂ intake were studied. Results: GSD patients had significantly higher plasma vitamin B₁₂ concentrations than healthy controls (p = 0.0002). Plasma vitamin B₁₂ concentration remained elevated in GSD patients irrespective of vitamin B₁₂ intake. Plasma vitamin B₁₂ concentrations correlated negatively with triglyceride levels, whereas no correlations were detected with liver transaminase activities (GOT and GPT) in GSD patients. Merging biomarker data of healthy controls and GSD patients showed a positive correlation between vitamin B₁₂ status and liver function, which suggests complex biomarker associations. A combined analysis of biomarkers permitted a reliable clustering of healthy controls versus GSD patients. Conclusions: Elevated plasma concentration of vitamin B₁₂ (irrespective of B₁₂ intake) is a common finding in patients with hepatic GSD. The negative correlation of plasma vitamin B₁₂ with triglyceride levels suggests an influence of metabolic control on the vitamin B₁₂ status of GSD patients. Elevated vitamin B₁₂ was not correlated with GOT and GPT in our cohort of GSD patients. Merging of data from healthy controls and GSD patients yielded positive correlations between these biomarkers. This apparent dichotomy highlights the intrinsic complexity of biomarker associations and argues against generalizations of liver disease and elevated vitamin B₁₂ in blood. Further studies are needed to determine whether the identified associations are causal or coincidental, and the possible impact of chronically elevated vitamin B₁₂ on GSD.

Higher vitamin B12 levels in neurodevelopmental disorders than in healthy controls and schizophrenia: A comparison among participants between 2 and 53 years

Recent studies suggest that both high and low levels of vitamin B12 (vitB12) may have negative health impacts. We measured VitB12 in patients with the Neurodevelopmental disorders (ND) (n = 222), comprised of Autism Spectrum Disorders, specific Developmental disorders, and Intellectual Disability (aged 2-53 years), schizophrenia (n = 401), and healthy controls (HC) (n = 483). Age-and gender-adjusted vitB12 z-scores were calculated by comparisons with a reference population (n = 76 148). We found higher vitB12 in ND (median 420 pmol/L, mean z-score: 0.30) than in HC (316 pmol/L, z-score: 0.06, P < .01) and schizophrenia (306 pmol/L, z-score: -0.02, P < .001), which was significant after adjusting for age, gender, vitB12 supplement, folate, hemoglobin, leukocytes, liver, and kidney function (P < .02). In ND, 20% (n = 44) had vitB12 above 650 pmol/L, and 1% (n = 3) had below 150 pmol/L (common reference limits). In 6.3% (n = 14) of ND, vitB12 was above 2SD of mean in the age-and gender-adjusted reference population, which was more frequent than in HC (n = 8, 1.6%), OR: 4.0, P = .001. Low vitB12 was equally frequent as in HC, and vitB12 z-scores were equal across the age groups. To conclude, vitB12 was higher in ND than in HC and schizophrenia, suggesting a specific feature of ND, which warrants further studies to investigate the underlying mechanisms.

Blood concentrations of vitamins B1, B6, B12, C and D and folate in palliative care patients: Results of a cross-sectional study

Objective

The main purpose of palliative care is symptom relief. Frequently, the symptoms of patients requiring palliative care are the same as common symptoms of vitamin deficiency (e.g. pain, weakness, fatigue, depression). The study aim was to investigate whether patients in palliative care are vitamin deficient.

Method

This was a monocentre cross-sectional study. Patients attending the palliative care unit of a general hospital in Germany from October 2015 to April 2016 were examined for vitamin blood concentrations and symptoms. Data were analysed using univariate analysis and bivariate correlations.

Results

Data were available from 31 patients. Vitamin D3 deficiency (<62.5 nmol/L) affected 93.5% of patients, vitamin B6 deficiency (<4.1 ng/mL) 48.4%, vitamin C deficiency (<4.5 mg/L) 45.2%, vitamin B1 deficiency (<35 µg/L) 25.8% and vitamin B12 deficiency (<193 pg/mL) 12.9%. There was a significant negative correlation between vitamin B1 ranges and pain (r = −0.384) and depression (r = −0.439) symptoms.

Conclusion

All patients showed a deficiency in at least one of the measured vitamins; 68% had concurrent deficiencies in >1 vitamin. A follow-up study using validated questionnaires and a larger sample is needed to investigate the effects of targeted vitamin supplementation on quality of life and symptom burden.

Association of vitamin D and vitamin B12 with cognitive impairment in elderly aged 80 years or older: a cross-sectional study

BACKGROUND

The present study aimed to assess the association of vitamin D and vitamin B₁₂ with cognitive impairment in elderly people.

METHODS

The data were obtained from a cross-sectional study that included individuals aged 80 years or older living in the urban and rural areas of the cities of Siderópolis and Treviso in the state of Santa Catarina, Brazil. In total, 165 elderly people were included in the analysis. The outcome of cognitive decline was assessed by the Mini-Mental State Examination. Vitamin D and vitamin B₁₂ levels were measured from blood samples. The socio-demographic, anthropometric and health variables used in the analysis were collected from a questionnaire. Crude and adjusted analyses of the relationship between vitamins D and B₁₂ and cognitive decline were performed using a Poisson regression model.

RESULTS

The prevalence of cognitive decline was 35.2%. In the adjusted model, individuals who had vitamin D levels >19 ng mL^-1 showed a lower prevalence of cognitive decline (prevalence ratio = 0.59; 95% confidence interval = 0.39-0.87). Those participants who had vitamin B₁₂ levels of ≥496 pg mL^-1 had a higher prevalence of cognitive decline (prevalence ratio = 1.90; 95% confidence interval = 1.08-3.36).

CONCLUSIONS

The present study showed that individuals aged ≥80 years who had vitamin D levels of ≤18 ng mL^-1 had a higher prevalence of cognitive decline even after adjustment for potential confounders. In addition, the study demonstrated that vitamin B₁₂ levels of ≥496 pg mL^-1 in this population were also a risk factor for cognitive decline. A cross-sectional analysis does not enable the inference of a cause-effect relationship and additional studies are needed to understand these relationships.

Autoimmune mechanisms in pernicious anaemia & thyroid disease

Pernicious anaemia (PA) and some types of thyroid disease result from autoimmune processes. The autoimmune mechanisms in these conditions have not been fully elucidated. This review discusses the autoimmune mechanisms involved in PA and how these affect diagnosis and disease progression. In addition to gastric antibodies, antibodies to the vitamin B12 binding protein transcobalamin which can result in high serum B12 levels are also addressed with regard to how they affect clinical practice. The role of autoimmune susceptibility is investigated by comparing PA to one of its most common comorbidities, autoimmune thyroid disease (AITD). Thyroid disease (although not exclusively AITD) and B12 deficiency are both also implicated in the pathology of hyperhomocysteinemia, an elevated homocysteine in plasma. Since hyperhomocysteinemia is a risk factor for cardiovascular occlusive disease, this review also addresses how thyroid disease in particular leads to changes in homocysteine levels.