Comparison of three methods for measuring vitamin B 12 in serum: radioisotopic, euglena gracilis and Lactobacillus leichmannii

Cobalamin and folate deficiencies among children in the age group of 12-59 months in India

BACKGROUND

Anemia is a major public health problem among children under 5 years of age in India. Cobalamin and folate deficiencies play an important role in the etiology of anemia. This study was done to assess the prevalence of cobalamin and folate deficiencies among children in the age group of 12-59 months.

METHODS

A community-based cross-sectional study was conducted. A total of 470 children were included. Non-fasting venous blood samples were collected from each child for the estimation of serum cobalamin and folate levels. Pattern of dietary consumption of the each child was assessed with the help of the food frequency questionnaire (FFQ) method.

RESULTS

The median levels (interquartile range) of serum cobalamin (n = 469) and folate (n = 416) were found to be 275 (202-427) pg/ml and 3.02 (2.02-4.94) ng/ml, respectively. The overall prevalence of cobalamin and folate deficiencies was found to be 180/469 [38.4%; 95% Confidence Interval (CI): 34.1-42.8%] and 263/416 (63.2%; 95% CI: 58.5-67.7%), respectively.

CONCLUSIONS

A high prevalence of cobalamin and folate deficiencies was found in children under 5 years of age.

Prevalence of Folate, Ferritin and Cobalamin Deficiencies amongst Adolescent in India

Background:

In India, 60-90% of adolescent suffer from anemia. Studies have documented folate, ferritin, and cobalamin deficiencies to be the major causes of nutritional anemia. However, limited data is available on the prevalence of folate, ferritin, and cobalamin deficiencies amongst adolescent from India.

Objectives:

The present study was carried out to find out the magnitude of folate, ferritin, and cobalamin deficiencies amongst adolescent of 11-18 years of age in National Capital Territory (NCT) of Delhi, India.

Materials and Methods:

A cross-sectional, school-based study was conducted in NCT of Delhi, India in the year 2010-2011. About 347 adolescent belonging to low- (LIG), middle- (MIG), and high-income groups (HIG) were selected using the probability proportionate to size (PPS) sampling methodology. Serum ferritin, serum folate, and serum cobalamin levels were determined by the enzyme-linked immunosorbent assay (ELISA) method, radioimmunoassay (RIA) method, and radioisotopic method, respectively. Hemoglobin (Hb) estimation was done by cyanmethemoglobin method in all the blood samples collected.

Results:

The prevalence of deficiency of ferritin in HIG, MIG, and LIG categories of adolescent was found to be 52.9, 67, and 58.8%, respectively. In the HIG, MIG, and LIG categories of adolescent, the prevalence of folate deficiency was 22.5, 40.4, and 52.2%, respectively. The prevalence of deficiency of cobalamin in HIG, MIG, and LIG categories of adolescent was 47.1, 80.7 and 87.5%, respectively. About 48, 66.1, and 68.4% of adolescent in the HIG, MIG, and LIG categories, respectively had Hb levels less than 12 g/dL and were found to be suffering from anemia.

Conclusions:

A high prevalence of anemia existed along with deficiency of ferritin, cobalamin, and folate amongst adolescent. The strategies for prevention of anemia amongst adolescent in India should also include cobalamin along with iron and folate supplementation for prevention and control of nutritional anemia. Primary care physicians should suspect all the three causes for anemia.

Vitamin B12 as a modulator of gut microbial ecology

The microbial mechanisms and key metabolites that shape the composition of the human gut microbiota are largely unknown, impeding efforts to manipulate dysbiotic microbial communities toward stability and health. Vitamins, which by definition are not synthesized in sufficient quantities by the host and can mediate fundamental biological processes in microbes, represent an attractive target for reshaping microbial communities. Here, we discuss how vitamin B12 (cobalamin) impacts diverse host-microbe symbioses. Although cobalamin is synthesized by some human gut microbes, it is a precious resource in the gut and is likely not provisioned to the host in significant quantities. However, this vitamin may make an unrecognized contribution in shaping the structure and function of human gut microbial communities.

Elevated serum homocysteine as a predictor for vitamin B12 or folate deficiency

Tissue deficiency of vitamin B12 and folate results in an increase in serum homocysteine (sHcy). We have measured sHcy in patients with reduced serum vitamin B12 and/or red cell folate (RCF) to determine its usefulness as a discriminant for the diagnostic interpretation of reduced vitamin levels. Of 3846 patients who had serum vitamin B12 and RCF assayed, 335 (9%) had reduced vitamin levels. Multivariate analysis showed a significant association between sHcy and serum creatinine (p = 0.0001), positive intrinsic factor (IF) antibody or neutrophil hypersegmentation (NHS) (p = 0.001), increased MCV (p = 0.014) and low RCF (p = 0.025) but no relationship with the level of serum vitamin B12 or haemoglobin. After censoring the patients with renal impairment (n = 54), the distribution of the remaining 72 patients with elevated sHcy was 37/151 (25%) with low serum vitamin B12 with or without low RCF and 35/130 (27%) with low RCF alone. sHcy correctly identified response to vitamin therapy in 33/35 (94%) patients who had adequate parameters to assess response. The positive predictive values of IF antibody/NHS, macrocytosis and/or low RCF for elevated sHcy were 100% and 34% respectively. Twenty-four percent of patients with a low serum vitamin B12 and elevated sHcy had no abnormal haematologic parameters as determined by the routine laboratory staff. These data suggest that the usefulness of measuring sHcy in a routine diagnostic setting is limited and a careful review of the peripheral blood for macrocytosis and NHS plus determination of RCF may be a more cost-effective process than sHcy assay in most instances to determine the presence of tissue deficiency.

Megaloblastic anaemia, cobalamin, and folate

Developments relating to cobalamin and folate are reviewed. Current work on the relations between these two coenzymes are discussed, particularly those that have emerged in studies using nitrous oxide, which inactivates cobalamin.

Longitudinal follow-up of chronic hemodialysis patients without vitamin supplementation

Vitamin supplementation for dialysis patients is still controversial. In our study, we followed longitudinally over a period of a year, 15 patients on chronic hemodialysis who were deprived of vitamin supplementation. Microbiological assays were used to determine the levels of five vitamins of the B group (folate, niacin, B12, B6, and thiamine). Vitamin C was measured chemically. During the observation period when vitamins were not supplemented, a marked drop of many of these vitamins in blood levels were encountered. For vitamins B12 and C, the plasma levels remained within the normal range in all the subjects studied. For the other vitamins, the blood levels were found to be low in a few patients. Our data suggest that vitamin supplementation is probably not needed in most stable hemodialysis patients as it is recommended now, and that perhaps, if supplementation is indicated, less should be given than is presently prescribed. Further research is needed in this area.

Human serum vitamin B12 assay methods--a review

The clinical importance of a reliable human serum vitamin B12 assay to aid the diagnosis of pernicious anemia (PA) cannot be overemphasized. Our review of the literature indicates that a reference method for the quantitation of serum vitamin B12 (serum B12) with the required accuracy, precision and rapidity has not been reported to-date. Controversies, debates and criticisms over human serum B12 assays (especially commercial kits) have been common-place. Various methods of quantitation of B12 reviewed in this communication include: microbiological, radioisotopic, high-performance liquid chromatography (HPLC) and the most recent radioimmunoassay (RIA) techniques. This review attempts to provide awareness of the limitations of these methods and establishes the base for eventual development of a B12 reference method in our laboratory.

Disorders of cobalamin metabolism

Recent developments in our knowledge of the biochemistry and metabolism of cobalamin have given us some insight into clinical disorders. N2O, which easily induces cobalamin deficiency, both in vivo and in vitro, has greatly contributed to the investigation of the cobalamin deficient state, especially in relation to folate and amino acid metabolism. Demonstration of the cobalamin analog in human serum and a new enzyme which requires cobalamin as a coenzyme has led to recent increased interest in this field. The disorders of cobalamin metabolism will be summarized briefly as well as those areas currently of particular interest.

Separation of cobalamin analogues in human sera binding to intrinsic factor and to R-type vitamin B12 binders

Intrinsic factor (IF) and cobalamin-R-binding protein (R-binder) linked to polyacrylamide beads were used to absorb cobalamins from solutions and serum extracts. Both binding agents were equally effective in removing [57Co]B12 from aqueous solution. IF was more effective than R-binder in removing [57Co]B12 added to a serum extract. All endogenous cobalamins detectable in serum by saturation analysis assay were removed by absorption onto R-binder. Absorption with IF removed microbiologically-active cobalamins but left behind analogues assayable with an R-binder. However, when absorption with IF was continued the concentration of R-binding cobalamins steadily declined indicating that IF bound both types of cobalamins through the binding was less avid for the microbiologically-inactive analogues than for microbiologically-active cobalamins. Finally, the R-binding analogues in serum were carried on transcobalamin I and none was detectable on transcobalamin II. The absorption studies establish the presence of two types of cobalamins one binding preferentially to IF and the other preferentially to R-binder. Only the former is detected by microbiological assay.

Use of an improved E. coli method for the measurement of cobalamin in serum: comparison with the E. gracilis assay results

Owing to the higher serum cobalamin results that are obtained by R-binder radioisotopic dilution assay compared to microbiological assays (E. gracilis and L. leichmannii) it was suggested that serum contained a cobamide(s) that could not be detected by the more specific microbiological assays and that a much less specific test organism, which responds to most naturally occurring cobamides, such as the cobamide-dependent E. coli mutant, might respond to these cobamide(s) in serum. In an attempt to investigate this possibility an improved and simplified E. coli assay for the measurement of cobamide in serum was developed. The method is described, and the results obtained in normal subjects, in patients with megaloblastic anemia, and in anaemic pregnant women not suffering from megaloblastic anaemia are reported and compared with E. gracilis assay results.

Comparison of serum vitamin B12 estimation by saturation analysis with intrinsic factor and with R-protein as binding agents

It has been reported that serum vitamin B12 levels assayed by saturation analysis methods may give misleadingly high results, so much so that the diagnosis of vitamin B12 deficiency may be obscured. This defect was ascribed largely to assays using a vitamin B12 binder other than pure intrinsic factor. To test out this hypothesis two assays were set up, one using saliva (non-intrinsic factor R-binder) and the other using human gastric (intrinsic factor) as B12-binding agents. Both assays were able to differentiate sera from patients with pernicious anaemia from those from control subjects. Published results accumulated over the past 10 years indicate that properly designed and performed saturation analysis vitamin B12 assays are as reliable as microbiological assay methods for detecting low serum B12 levels. The failure of some methods to do does not appear to be due to the nature of the B12-binding agent.

Changes in serum levels of cobalamin and cobalamin analogues in folate deficiency

The recent introduction of radioassays for 'true' cobalamin, as opposed to cobalamin and its analogues, has resulted in significantly lower levels of cobalamin being found in patients with folate deficiency. In study of 81 patients, cobalamin analogue levels were found to increase and cobalamin to decrease as red cell folates decreased. Cobalamin absorption studies in 15 patients with low cobalamin and folate levels were found to be normal in 10 patients, all of whom demonstrated high levels of analogues relative to true cobalamin. We have found that the mean serum cobalamin increased from 210 ng/l (range 100-380) to 309 (150-470) and analogues fell from 226 ng/l (150-280) to 127 (65-190) in folate deficient patients when treated with folic acid. It appears that cobalamin analogue concentrations are increased in folate deficiency, and that in these patients treatment with folic acid alone may correct both the low cobalamin and the high analogue levels.

Interlaboratory comparison of serum vitamin B12 assay

The results have been compared of microbiological and radioisotope dilution (RID) assay of serum vitamin B12 by participants in national interlaboratory trials in Britain. There was wide variation between the individual participants, especially marked in the L. leichmannii microbiological assay and in the RID methods, whereas excellent correlation, reproducibility, and recovery were obtained in reference laboratories by microbiological assay with both E. gracilis and L. leichmannii. In general, RID gave higher results than microbiological assay. The need for suitable reference sera is emphasised.

An evaluation of commercial radioisotope methods for the determination of folate and vitamin B12

Five commercial kits for the determination of folate and six kits for the determination of vitamin B12 were investigated. Their performance has been compared with microbiological methods for the two vitamins and with a non-commercial radioisotopic method for B12. The results show the importance of the determination of the reference range for an individual laboratory for each method. The precision of the kits varied appreciably, as did their performance using specimens from patients with different haematological disorders. In particular, certain kits failed to detect all patients with pernicious anaemia. The relative accuracy of the kits was assessed. Various factors which should be taken into account in the final selection of a satisfactory kit are discussed.

Tissue vitamin B-12 assay by a radioisotope dilution technique

A method is described for the measurement of vitamin B-12 (B-12) in solid tissues by radioisotope dilution (RID) assay. The method is a modivication using double extraction of a serum B-12 RID assay which uses chicken serum as the B-12 binder. The method was developed and tested using human and bat liver specimens. Double extraction was shown to be more efficient than single extraction, and resulted in complete release of endogenous liver [57Co] B-12 administered to bats. Results using the RID assay in 16 humans and 17 bat liver specimens were compared with those obtained using the Lactobacillus leichmannii microbiological assay. Correlation was good, but the RID assay gave higher results using the microbiological assay appear to be due to inadequate extraction of B-12 from tissues.

Extraction of serum vitamin B12 for radio-isotopic and Lactobacillus leichmannii assay

The protein precipitates discarded during the extraction process of the Lactobacillus leichmannii vitamin B12 assay have been shown to contain significant amounts of vitamin B12. This loss of vitamin B12 provide a satisfactory explanation for many of the descrepancies between the serum vitamin B12 values obtained by the L. leichmannii method and the radio-isotopic method of Raven et al (1969). It is possible to produce lower results by the method of Raven et al (1969)by incorporating into that method the L. leichmannii extraction process; it is also possible to produce higher results by the L. leichmannii method using a papain extraction process.

Comparison of results of microbiologic and radioisotopic assays for serum vitamin B12 during pregnancy

The serum vitamin B12 level falls progressively during pregnancy, when measured either by microbiologic assay or by a radioisotope dilution technique. The concentration of the vitamin assayed by radioisotope dilution was consistently higher than the value obtained by microbiologic assay. This discrepancy was greatest in early pregnancy and decreased as the duration of pregnancy increased. These results add further evidence to the hypothesis that changes in serum binders for vitamin B12 are of major significance in the pathogenesis of the observed fall in serum levels of the vitamin during pregnancy.

Use of radioisotope techniques in the clinical evaluation of patients with megaloblastic anemia

Because virtually all cases of vitamin B12 deficiency seen in this country are due to malabsorption, the availability of radioactive vitamin B12 for direct measurement of absorption of this essential nutrient has proved to be of great clinical value. These tests are useful not only in demonstrating vitamin B12 malabsorption but also often in defining the pathophysiological mechanism responsible for this abnormality. The urinary excretion test of Schilling remains the most useful test for vitamin B12 absorption. Minor precautions and modifications in technique make the test results more reliable and easier to interpret. The 8-hr plasma test for vitamin B12 absorption can no longer be considered acceptable. Some patients with vitamin B12 malabsorption have results in the normal range when studied by this method. Serum vitamin B12 assays utilizing radioactive vitamin B12 and the isotope dilution principle are not widely used and are useful screening tests. Low normal or borderline results observed in patients with clinical evidence suggestive of vitamin B12 deficiency should be interpreted with caution or confirmed by radioactive vitamin B12 absorption studies. Radioactive vitamin B12 can also be used for rapid, reliable assay of gastric intrinsic factor, antibody to intrinsic factor and unsaturated vitamin B12 serum. Methods using radioactive folate compounds for similar in vivo and in vitro studies are not yet applicable for routine use in nuclear medicine laboratories.

Experience with a commercial kit for the radioisotopic assay of vitamin B12 in serum: the Phadebas B12 test

The first commercial kit for the radioisotopic assay of vitamin B(12) in serum-the Phadebas B(12) Test produced higher values than the radioisotopic method of Raven, Robson, Walker, and Barkham (1969) and the Lactobacillus leichmannii microbiological assay. Its normal range was 300-1100 pg/ml and its reproducibility was similar to that of the other radioisotopic method. It should be possible to lower the results obtained by the Phadebas method by modifying its standard curve and to reduce the time taken for the assay by shortening its incubation period.

An automated microbiological method for the measurement of vitamin B12

An automated method for the microbiological assay of vitamin B(12) is described. A chloramphenicol-resistant strain of Lactobacillus leichmannii is used as the test organism and this eliminates the need for sterilization or aseptic addition. Precipitation of the serum protein is avoided by dilution of the serum with a glutamic/malic acid solution before heating the preparation to free the vitamin B(12). Tests can be set up at a rate of 80 an hour and after incubation they can be read at 160 an hour. By interfacing a programmed electronic calculator directly with the Mecolab M which is used for the assays, results are printed directly in ng/l.