Reference intervals and stability of haptocorrin and holotranscobalamin in Danish children and elderly

BACKGROUND

Haptocorrin (HC) and holotranscobalamin (holoTC) carry vitamin B12 (B12) in the circulation and can be useful biomarkers for evaluating B12 status. The concentration of both proteins depends on age, but data on reference intervals for children and the elderly are sparse. Similarly, not much is known about the effect of preanalytical factors.

METHODS

HC plasma samples from healthy elderly > 65 years (n = 124) were analysed, and both HC and holoTC were analysed in paediatric serum samples ≤ 18 years (n = 400). Furthermore, we investigated assay precision and stability.

RESULTS

HC and holoTC were effected by age. We established reference intervals for HC: 2-10 years, 369-1237 pmol/L; 11-18 years, 314-1128 pmol/L; 65-82 years, 242-680 pmol/L and for holoTC: 2-10 years, 46-206 pmol/L; 11-18 years, 30-178 pmol/L. Analytical coefficients of variations of 6.0-6.8% and 7.9-15.7% were found for HC and holoTC, respectively. HC were affected when stored at room temperature and by freeze/thaw. HoloTC was stable at room temperature and after delayed centrifugation.

CONCLUSION

We present novel 95% age-related reference limits for HC and HoloTC in children, and for HC both in children and elderly. Moreover, we found HoloTC to be fairly stable when stored, whereas HC was more vulnerable to preanalytical factors.

Seminal but not Serum Levels of Holotranscobalamin are Altered in Morbid Obesity and Correlate with Semen Quality: A Pilot Single Centre Study

Vitamin B12 (cobalamin) is an essential cofactor in the one-carbon metabolism. One-carbon metabolism is a set of complex biochemical reactions, through which methyl groups are utilised or generated, and thus plays a vital role to many cellular functions in humans. Low levels of cobalamin have been associated to metabolic/reproductive pathologies. However, cobalamin status has never been investigated in morbid obesity in relation with the reduced semen quality. We analysed the cross-sectional data of 47-morbidly-obese and 21 lean men at Careggi University Hospital and evaluated total cobalamin (CBL) and holotranscobalamin (the active form of B12; holoTC) levels in serum and semen. Both seminal and serum concentrations of holoTC and CBL were lower in morbidly obese compared to lean men, although the difference did not reach any statistical significance for serum holoTC. Seminal CBL and holoTC were significantly higher than serum levels in both groups. Significant positive correlations were observed between seminal holoTC and total sperm motility (r = 0.394, p = 0.012), sperm concentration (r = 0.401, p = 0.009), total sperm number (r = 0.343, p = 0.028), and negative correlation with semen pH (r = -0.535, p = 0.0001). ROC analysis supported seminal holoTC as the best predictor of sperm number (AUC = 0.769 ± 0.08, p = 0.006). Our findings suggest that seminal rather than serum levels of holoTC may represent a good marker of semen quality in morbidly obese subjects.

Foods and Supplements Associated with Vitamin B12 Biomarkers among Vegetarian and Non-Vegetarian Participants of the Adventist Health Study-2 (AHS-2) Calibration Study

To investigate the association between plasma concentration of vitamin B₁₂ and B₁₂ intake from supplements, fortified foods, and animal source foods among vegetarians and non-vegetarians, we conducted a cross-sectional analysis among 728 participants of the Adventist Health Study 2 (AHS-2) calibration study. The median age of participants was 58 years, 65.4% were female, and 50.3% were White. We used six 24 h dietary recalls to measure B₁₂ intake, serum vitamin B₁₂, and holotranscobalamin (holoTC) concentration. B₁₂ supplements had a significantly positive association with plasma B₁₂ among all subjects (p trend < 0.001), especially among vegans and lacto-ovo vegetarians (p trend < 0.001). Among non-users of B₁₂ supplements, B₁₂ intake from milk substitutes was significantly positively associated with holoTC (p trend < 0.004) and serum B12 (p trend < 0.030). In non-vegetarians, holoTC was significantly positively associated with B₁₂ intake from eggs, while serum B₁₂ was significantly positively associated with B₁₂ intake from milk in the upper tertile compared to the lower, and B₁₂ intake from meat in the middle compared to the lower tertile intake (p < 0.011). Supplements containing B₁₂ followed by B₁₂ intake from milk substitutes were significant contributors of plasma vitamin B₁₂ concentration.

Early changes in vitamin B12 uptake and biomarker status following Roux-en-Y gastric bypass and sleeve gastrectomy

BACKGROUND & AIMS

Bariatric surgery increases the risk of micronutrient deficiencies, including vitamin B12 (B12) deficiency. We analysed early changes in biomarkers of B12 status following bariatric surgery.

METHODS

We prospectively included adult patients (n = 27) referred for either Roux-en-Y Gastric Bypass (RYGB) (n = 19) or Sleeve Gastrectomy (SG) (n = 8). Blood samples were drawn before surgery and 2 and 6 months following surgery for measurement of B12, holotranscobalamin (holoTC), and methylmalonic acid (MMA). The B12 absorption capacity was estimated from the increase in plasma holoTC two days after a standardised oral B12 challenge.

RESULTS

B12 status decreased following both RYBG and SG. While a decrease in plasma B12 was not evident until 6 months postoperatively, we observed a statistically significant decrease in plasma holoTC and increase in MMA already 2 months postoperatively. These changes were more pronounced at 6 months post surgery. Correspondingly, the B12 absorption capacity was decreased following surgery.

CONCLUSIONS

HoloTC and MMA were superior to B12 to detect early changes in B12 status following bariatric surgery. Our data challenge the current concept that liver B12 stores secure long-term maintenance of B12 status. They indicate that B12 treatment in pharmacological doses may be warranted immediately after surgery.

Measurement of total Transcobalamin employing a commercially available assay for Active B12

INTRODUCTION

Vitamin B12 deficiency is mostly caused by insufficient gastro-intestinal absorption and in rare conditions by Transcobalamin (TC) deficiency. Unsaturated Transcobalamin (apoTC) can be measured by a binding assay using radiolabeled cobalamin. The Active B12 test analyzes saturated Transcobalamin (holoTC) and we hypothesize that this test can be used to measure total TC by additional in vitro saturation with cobalamin.

METHODS

Serum was saturated in vitro (16 times dilution) with a cyanocobalamin solution and total TC was selectively measured with the Abbott Active B12 test. ApoTC was calculated by subtracting endogenous holoTC from total TC after correction for dilution. Linearity was determined with a pool serum dilution series. Precision was investigated according to the CLSI EP15 protocol. Method comparison was performed against a binding assay using radiolabeled cobalamin. Reference values were determined in 100 healthy controls.

RESULTS

The method was linear in the range of 240 to 1933pmol/L (R²=0.997, lack of fit F=1.61). Precision of low- and high-pool total TC in serum were; 5.2% and 4.3% respectively. Method comparison against a radiolabeled cobalamin binding assay showed a proportional bias of 30% (y=0.70x+126). Total TC reference values were determined at 500-1276pmol/L.

CONCLUSION

We describe a rapid method to quantify total TC, which can be implemented on routine platforms using commercial Active B12 tests. In addition, apoTC can be assessed by subtracting endogenous holoTC concentration which can be measured in the same run, securing the same calibration level for all three parameters (holoTC, apoTC and total TC). This method is applicable in clinical diagnostics and in larger epidemiological studies.

Folate and Vitamin B12-Related Biomarkers in Relation to Brain Volumes

AIM

We investigated cross-sectional associations between circulating homocysteine, folate, biomarkers of vitamin B₁₂ status and brain volumes. We furthermore compared brain volumes of participants who received daily folic acid and vitamin B₁₂ supplementation with participants who did not.

METHODS

Participants of the B-PROOF study (n = 2919) were assigned to 400 µg folic acid and 500 µg vitamin B₁₂, or a placebo. After two years of intervention, T₁-weighted magnetic resonance imaging (MRI) scans were made in a random subsample (n = 218) to obtain grey and white matter volume, and total brain volume (TBV). Plasma homocysteine, serum folate, vitamin B₁₂, holotranscobalamin, and methylmalonic acid concentrations were measured.

RESULTS

Multiple linear regression analyses showed inverse associations between plasma homocysteine with TBV (β = -0.91, 95% CI -1.85-0.03; p = 0.06) and between serum folate and TBV (β = -0.20, 95% CI -0.38, -0.02; p = 0.03). No significant associations were observed for serum vitamin B₁₂ and holotranscobalamin. Fully adjusted ANCOVA models showed that the group that received B-vitamins had a lower TBV (adjusted mean 1064, 95% CI 1058-1069 mL) than the non-supplemented group (1072, 95% CI 1067-1078 mL, p = 0.03).

CONCLUSIONS

Results were contradictory, with higher Hcy levels associated with lower TBV, but also with higher folate levels associated with lower TBV. In addition, the lack of a baseline measurement withholds us from giving recommendations on whether folic acid and vitamin B₁₂ supplementation will be beneficial above and beyond normal dietary intake for brain health.

An International Standard for holotranscobalamin (holoTC): international collaborative study to assign a holoTC value to the International Standard for vitamin B12 and serum folate

BACKGROUND

Investigation of possible B12 and folate deficiencies requires measurement of these vitamins in serum. There is evidence that holotranscobalamin (holoTC), the active portion of B12 available to cells, is a more specific marker of early B12 deficiency than total B12. The availability of immunoassays for holoTC prompted an international collaborative study to assign a holoTC value to the World Health Organization (WHO) 1st International Standard (IS) for vitamin B12 and serum folate, 03/178.

METHODS

The IS, 03/178, and three serum samples with different holoTC levels were assayed by 12 laboratories in eight countries using manual and automated immunoassays for holoTC; one laboratory additionally performed an in-house assay. Fourteen sets of data were analysed.

RESULTS

Overall, the IS, 03/178, and the three serum samples demonstrated assay linearity and parallelism. An overall geometric mean (GM) holoTC value of 106.8 pmol/L was obtained for 03/178, with an inter-laboratory geometric coefficient of variation (GCV) of 10.5%. There was a reduction in inter-laboratory variability when the holoTC levels in the serum samples were determined relative to the IS with an assigned holoTC value rather than to the assays' calibration. Accelerated degradation studies showed that 03/178 was sufficiently stable to serve as an IS for holoTC.

CONCLUSIONS

The WHO Expert Committee on Biological Standardization endorsed the proposal to assign a holoTC value of 107 pmol/L to 03/178, corresponding to 0.107 pmol per ampoule, for use as the 1st IS for vitamin B12, serum folate, and holoTC.

Biochemical Identification of Vitamin B12 Deficiency in a Medical Office

BACKGROUND

A vitamin B12 deficiency can be an underlying cause or a deteriorating factor in several diseases. Nevertheless, early identification of such a deficiency remains a problem. Holotranscobalamin (HTC) is presently considered to be the gold standard. We tested the predictive power of other B12 parameters by comparing them with HTC.

METHODS

The blood of 77 patients from a medical office was tested for HTC, total B12 (CLIA [chemiluminescent immunoassay] and MTP [microbiological test with microtitre plates]), MMA (methylmalonic acid), HCY (homocysteine), and MCV (mean cell volume). The parameters were correlated and sensitivity, specificity, PPV (positive predictive value), NPV (negative predictive value), LR+ (positive likelihood ratio), and LR- (negative likelihood ratio) in comparison to HTC were determined. A ROC analysis was also performed.

RESULTS

At a cutoff value of 35 pmol/L for HTC, the total B12 CLIA (cutoff 211 ng/L) qualified 53% of individuals as having a B12 deficiency. The total B12 MTP (cutoff 288 ng/L) classified 71% as having a B12 deficiency. Specificity was similar in both cases (CLIA, 93%; MTP, 95%). With a cutoff value of 10 µmol/L for homocysteine, the best negative prediction was achieved. MVA has a low sensitivity (41%) and a high specificity (90%). Based on the ROC analysis, which indicated superiority of the B12-MTP, the reference levels of B12-CLIA and B12-MTP were raised to 304 and 368 ng/L, respectively. Thus, a probable B12 deficiency was identified in 94% of cases with either method and with a comparable specificity.

CONCLUSIONS

If total B12 is applied to identify B12 deficiency, the cutoff values should be elevated to 304 (B12-CLIA) and 368 ng/L (B12-MTP) to improve the predictive power. The negative-predictive power of HCY can be useful in daily routine. HTC has a broad grey area of uncertainty and MMA should only be applied as a confirmatory test.

Vitamin B12 and homocysteine status during pregnancy in the metformin in gestational diabetes trial: responses to maternal metformin compared with insulin treatment

AIM

The aim of the study is to compare the effects of metformin and insulin treatment for gestational diabetes mellitus (GDM) on vitamin B12 and homocysteine (Hcy) status.

METHODS

Women with GDM, who met criteria for insulin treatment, were randomly assigned to metformin (n = 89) or insulin (n = 91) in the Adelaide cohort of the metformin in gestational diabetes (MiG) trial. Fasting serum total vitamin B12 (TB12), holotranscobalamin (HoloTC), a marker of functional B12 status and plasma Hcy concentrations were measured at 20-34 weeks (at randomization) and 36 weeks gestation, then at 6-8 weeks postpartum.

RESULTS

Circulating TB12, HoloTC and Hcy were similar in both treatment groups at each time point. Women who were taking dietary folate supplements at randomization had higher serum TB12 and HoloTC at randomization than those not taking folate. Overall, serum TB12 fell more between randomization and 36 weeks gestation in the metformin group than in the insulin group (metformin: -19.7 ± 4.7 pmol/l, insulin: -6.4 ± 3.6 pmol/l, p = 0.004). The decrease in serum TB12 during treatment was greater with increasing treatment duration in metformin-treated (p < 0.001), but not in insulin-treated women.

CONCLUSIONS

Total, but not bioavailable, vitamin B12 stores were depleted during pregnancy to a greater extent in metformin-treated than in insulin-treated women with GDM, but neither analyte differed between groups at any stage. This adds further evidence supporting metformin as a safe alternative treatment to insulin in GDM. Further investigation is needed to evaluate whether women treated with metformin for longer periods in pregnancy require additional B12 or other supplementation.

Cobalamin analogues in humans: a study on maternal and cord blood

BACKGROUND

Haptocorrin (HC) carries cobalamin analogues (CorA), but whether CorA are produced in the body is unknown. All cobalamins (Cbl) to the foetus are delivered by the Cbl-specific protein transcobalamin (TC), and therefore analysis of cord serum for CorA may help to clarify the origin of CorA.

METHODS

HC-CorA were quantified in paired samples of cord serum from newborns and serum from mothers (n = 69).

RESULTS

The CorA-concentration was higher in cord serum (median = 380, range: 41-780 pmol/L) than in serum from the mothers (median = 160, range: 64-330 pmol/L), (p<0.0001). HPLC-analysis showed CorA-peaks with retention times of 13.5, 14,5 and 16.5 min in samples from both the mother and cord serum. The peak with retention time 16.5 min constituted 24% (mother) and 45% (cord serum) of the total amount CorA, and eluted as does dicyanocobinamide.

CONCLUSION

Our results support that CorA in the human body are derived from Cbl.

[Approaches to vitamin B12 deficiency]

A 28-year-old female vegetarian was referred to a specialist in internal medicine with persistent iron deficiency. Laboratory analysis revealed microcytic anaemia with low ferritin levels but normal total vitamin B12 levels. The red blood cell distribution width, however, showed a very wide variation in red blood cell sizes, indicating a coexisting vitamin B12 deficiency, which was confirmed by the low concentration of active vitamin B12. Another patient, a 69-year-old woman with a history of previous gastric surgery and renal insufficiency as a complication of diabetes mellitus, was suspected to be deficient in vitamin B12, as she had low total vitamin B12 levels and an accumulation of methylmalonic acid and homocysteine in her blood. Testing the total concentration of vitamin B12 alone has insufficient diagnostic accuracy and no accepted gold standard is available for diagnosing vitamin B12 deficiency. With the development of newer tests, such as measuring holotranscobalamin II (concentration of active vitamin B12), atypical and subclinical deficiency states can be recognized. A new approach to diagnosing vitamin B12 deficiency is presented, based upon these 2 case descriptions.

Vitamin B12 absorption judged by measurement of holotranscobalamin, active vitamin B12: evaluation of a commercially available EIA kit

BACKGROUND

Active vitamin B12 absorption is followed by an increase in holotranscobalamin (holoTC) upon loading with a high physiological dose of the vitamin (the CobaSorb test). This study evaluates the use of a newly launched EIA kit for measurement of holoTC (active B12) in relation to the CobaSorb test.

METHODS

Intra-assay imprecision and linearity of the EIA kit was examined, employing serum pools of increasing holoTC concentrations. For the CobaSorb test, holoTC was measured before and after loading with 3-times 9 μg of vitamin B12 employing both the in-house ELISA and the EIA kit (n=25).

RESULTS

The EIA kit showed an intra-assay CV between 2.2% and 5.8% for holoTC values ranging from 21 to 80 pmol/L. Employing diluted serum samples resulted in spurious high values of holoTC. The EIA kit performed well in relation to the CobaSorb test and classified the patients studied as capable of absorbing vitamin B12 (n=10) or not (n=15), as did the in-house ELISA.

CONCLUSIONS

The Active B12 (holoTC) EIA kit proved suitable for use with the CobaSorb test, but not for analysis of diluted serum samples.

Metabolic signs of vitamin B(12) deficiency in humans: computational model and its implications for diagnostics

Early diagnostics of cobalamin (Cbl, vitamin B(12)) deficiency is primarily based on measurements of the relevant metabolic markers in blood plasma--total B(12), specific Cbl-saturated transporter holo-transcobalamin (holoTC), and substrates of Cbl-dependent enzymatic reactions methylmalonic acid (MMA) and homocysteine (Hcy). Concentrations of B(12) and holoTC decrease whereas MMA and Hcy increase under deficiency. Yet, the results of individual tests are often contradictory and do not guarantee unambiguous diagnosis. The current work describes the metabolic manifestation of vitamin B(12) deficiency in terms of flux equations fitted to data sets from literature. The model mathematically connects all the markers and presents 4 independent measurements as a single point (x, y) in the combined coordinates x = (holoTC x B(12))((1/2)) and y = (1/2)log(10)(MMA x Hcy). Pairwise averaging compensates for the individual fluctuations of the markers caused by (1) irregular spikes of holoTC, (2) delayed change of the total plasma B(12) buffered by an internal Cbl depot, and (3) variations in the production/excretion velocities of MMA and Hcy. Bivariate distribution of the marker combinations (x, y) reveals several peaks of frequency in the analyzed mixed population. The peaks seem to represent the reference subgroups with different B(12) physiology and characteristic values of "wellness parameter": w = log(10)(holoTC(n)) + log(10)(B(12n)) - log(10)(MMA(n)) - log(10)(Hcy(n)), where concentrations are normalized (eg, MMA(n) = MMA/MMA(normal)). Dynamic response of the organism to B(12) intake is quantified and described as an additional analytical tool when classifying uncertain cases. The discussed mathematical approaches are of general applicability in diagnostics.

Assessment of vitamin B(12) absorption based on the accumulation of orally administered cyanocobalamin on transcobalamin

BACKGROUND

Vitamin B(12), or cobalamin (Cbl), is absorbed in the intestine and transported to the cells bound to transcobalamin (TC). We hypothesize that cyanocobalamin (CNCbl) is absorbed unchanged, thereby allowing measurement of the complex of CNCbl bound to TC (TC-CNCbl) to be used for studying the absorption of the vitamin.

METHODS

TC was immunoprecipitated from serum samples obtained from healthy donors at baseline and at 24 h after oral administration of three 9-microg CNCbl doses over 1 day. Cbl was released by treatment with subtilisin Carlsberg. The different forms of Cbl were isolated by HPLC and subsequently quantified with an ELISA-based Cbl assay.

RESULTS

At baseline, the median TC-CNCbl concentration was 1 pmol/L (range, 0-10 pmol/L); the intraindividual variation (SD) was 1.6 pmol/L (n = 31). After CNCbl administration, the TC-CNCbl concentration increased significantly (P = 0.0003, paired t-test), whereas no major changes were observed in any of the other Cbl forms bound to TC (n = 10). Only a moderate additional increase in TC-CNCbl was observed with prolonged (5 days) CNCbl administration (n = 10). We designed an absorption test based on measuring TC-CNCbl at baseline and 24 h after CNCbl intake and established a reference interval for the increase in TC-CNCbl (n = 78). The median absolute increase was 23 pmol/L (range, 6-64 pmol/L), and the relative increase was >3-fold.

CONCLUSIONS

Our data demonstrate that CNCbl is absorbed unchanged and accumulates on circulating TC. We suggest that measuring TC-CNCbl will improve the assessment of vitamin B(12) absorption.

Vitamin B12 and the risk of neural tube defects in a folic-acid-fortified population

BACKGROUND

Low maternal vitamin B(12) status may be a risk factor for neural tube defects (NTDs). Prior studies used relatively insensitive measures of B(12), did not adjust for folate levels, and were conducted in countries without folic acid food fortification. In Canada, flour has been fortified with folic acid since mid-1997.

METHODS

We completed a population-based case-control study in Ontario. We measured serum holotranscobalamin (holoTC), a sensitive indicator of B(12) status, at 15 to 20 weeks' gestation. There were 89 women with an NTD and 422 unaffected pregnant controls. A low serum holoTC was defined as less than 55.3 pmol/L, the bottom quartile value in the controls.

RESULTS

The geometric mean serum holoTC levels were 67.8 pmol/L in cases and 81.2 pmol/L in controls. There was a trend of increasing risk with lower levels of holoTC, reaching an adjusted odds ratio of 2.9 (95% confidence interval = 1.2-6.9) when comparing the lowest versus highest quartile.

CONCLUSIONS

There was almost a tripling in the risk for NTD in the presence of low maternal B(12) status, measured by holoTC. The benefits of adding synthetic B(12) to current recommendations for periconceptional folic acid tablet supplements or folic-acid-fortified foods need to be considered. It remains to be determined what fraction of NTD cases in a universally folate-fortified environment might be prevented by higher periconceptional intake of B(12).

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

Background: Impaired vitamin B12 function and decreased vitamin B12 status have been associated with neurological and cognitive impairment. Current assays analyze total vitamin B12 concentration, only a small percentage of which is metabolically active. Concentrations of this active component, carried on holotranscobalamin (holoTC), may be of greater relevance than total vitamin B12.

Methods: We compared the utility of serum holoTC with conventional vitamin B12 for detection of vitamin B12 deficiency in a population-based study of older people, using increased methylmalonic acid (MMA) concentrations as a marker of metabolic vitamin B12 deficiency in the overall population (n = 2403) and in subsets with normal (n = 1651) and abnormal (n = 752) renal function.

Results: Among all participants, 6% had definite (MMA &gt;0.75 μmol/L) and 16% had probable (MMA &gt;0.45 μmol/L) metabolic vitamin B12 deficiency. In receiver operating characteristic curves for detection of definite vitamin B12 deficiency, holoTC had a greater area under the curve (AUC) compared with vitamin B12 in all participants (0.85 vs 0.76; P &lt;0.001) and in subsets with normal (AUC: 0.87 vs 0.79; P &lt;0.001) and abnormal (AUC: 0.85 vs 0.74; P = 0.002) renal function. Similar findings were observed for detection of moderate vitamin B12 deficiency. Whereas the positive predictive value for both holoTC and vitamin B12 was greater for detection of probable than definite vitamin B12 deficiency, both tests were associated with more false-positive than true-positive test results.

Conclusions: HoloTC has a modestly superior diagnostic accuracy compared with conventional vitamin B12 for the detection of vitamin B12 deficiency, but neither test can be recommended to screen asymptomatic populations.

Holo-transcobalamin is an indicator of vitamin B-12 absorption in healthy adults with adequate vitamin B-12 status

BACKGROUND

It has been hypothesized that the response of holo-transcobalamin (holo-TC) to oral vitamin B-12 may be used to assess absorption. To develop a reliable clinical absorption test that uses holo-TC, it is necessary to determine the optimal timeline for vitamin B-12 administration and postdose assessment.

OBJECTIVE

The objective of this study was to assess the magnitude and patterns of change in the postabsorption response of holo-TC to oral vitamin B-12.

DESIGN

Adult (18-49 y) male and female participants (n = 21) with normal vitamin B-12 status were given three 9-mug doses of vitamin B-12 at 6-h intervals beginning early morning (baseline) on day 1. Blood was drawn at 17 timed intervals over the course of 3 d for the analysis of holo-TC and other indicators of vitamin B-12 status.

RESULTS

Mean holo-TC increased significantly (P < 0.001) from baseline at 6 h (11%) and 24 h (50%). TC saturation increased significantly (P < 0.001) from baseline at 12.5 h (33%) and 24 h (50%). The mean cobalamin concentration changed significantly (P < 0.001) from baseline at 24 h (15%) and 48 h (14%). The ratio of holo-TC to cobalamin increased significantly (P < 0.001) at 24 h (32%).

CONCLUSIONS

The greatest increase in holo-TC was observed 24 h after ingestion of three 9-mug doses of vitamin B-12. Our results indicate that a vitamin B-12 absorption test based on measurement of holo-TC after administration of three 9-mug doses of vitamin B-12 should run for 24 h.

Plasma holotranscobalamin compared with plasma cobalamins for assessment of vitamin B12 absorption; optimisation of a non-radioactive vitamin B12 absorption test (CobaSorb)

BACKGROUND

A recently developed non-radioactive vitamin B(12) absorption test (CobaSorb) was further explored to identify the best marker for reflection of vitamin B(12) absorption and to determine the duration of the test.

METHODS

Seventy-eight healthy individuals (age 21-81 years) were given three oral doses of 9 microg vitamin B(12) per day for 5 successive days. Non-fasting blood samples were collected on days 1 to 5 before administration of vitamin B(12) and on day 8. Cobalamins and holotranscobalamin were measured.

RESULTS

Performance of the vitamin B(12) absorption test was evaluated in individuals with holotranscobalamin or cobalamins below the 75% percentiles. We used a change greater than 2xCV(day-to-day) in holotranscobalamin (22%) and cobalamins (12%) to indicate a change caused by absorption of vitamin B(12). Among individuals with a baseline holotranscobalamin below the 75% percentile (<75 pmol/L, n=57), 98% had an increase in holotranscobalamin >22% from day 1 to day 3. In contrast, only 72% of the individuals with baseline cobalamins below the 75% percentile (<335 pmol/L, n=57) had an increase in cobalamins >12%.

CONCLUSIONS

In healthy individuals with baseline holotranscobalamin <75 pmol/L, vitamin B(12) absorption is well reflected by an increase in holotranscobalamin after 2 days administration of oral vitamin B(12).

Biomarkers of folate and vitamin B12 are related in blood and cerebrospinal fluid

BACKGROUND

B-vitamins (folate, B(12)) are important micronutrients for brain function and essential cofactors for homocysteine (HCY) metabolism. Increased HCY has been related to neurological and psychiatric disorders. We studied the role of the B-vitamins in HCY metabolism in the brain.

METHODS

We studied blood and cerebrospinal fluid (CSF) samples from 72 patients who underwent lumbar puncture. We measured HCY, methylmalonic acid (MMA), and cystathionine by gas chromatography-mass spectrometry; S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) by liquid chromatography-tandem mass spectrometry; and the B-vitamins by HPLC or immunoassays.

RESULTS

Concentrations were lower in CSF than serum or plasma for HCY (0.09 vs 9.4 micromol/L), SAH (13.2 vs 16.8 nmol/L), cystathionine (54 vs 329 nmol/L), and holotranscobalamin (16 vs 63 pmol/L), whereas concentrations in CSF were higher for MMA (359 vs 186 nmol/L) and SAM (270 vs 113 nmol/L; all P <0.05). CSF concentrations of HCY correlated significantly with CSF folate (r = -0.46), CSF SAH (r = 0.48), CSF-albumin (r = 0.31), and age (r = 0.32). Aging was also associated with lower concentrations of CSF-folate and higher CSF-SAH. The relationship between serum and CSF folate depended on serum folate: the correlation (r) of serum and CSF-folate was 0.69 at serum folate <15.7 nmol/L. CSF concentrations of MMA and holotranscobalamin were not significantly correlated.

CONCLUSIONS

CSF and serum/plasma concentrations of vitamin biomarkers are significantly correlated. Older age is associated with higher CSF-HCY and CSF-SAH and lower CSF-folate. These metabolic alterations may be important indicators of low folate status, hyperhomocysteinemia, and neurodegenerative diseases.

Effect of oral vitamin B-12 with or without folic acid on cognitive function in older people with mild vitamin B-12 deficiency: a randomized, placebo-controlled trial

BACKGROUND

Vitamin B-12 deficiency is associated with cognitive impairment in older people. However, evidence from randomized trials of the effects of vitamin B-12 supplementation on cognitive function is limited and inconclusive.

OBJECTIVE

The objective was to investigate whether daily supplementation with high doses of oral vitamin B-12 alone or in combination with folic acid has any beneficial effects on cognitive function in persons aged >/=70 y with mild vitamin B-12 deficiency.

DESIGN

In a double-blind, placebo-controlled trial, 195 subjects were randomly assigned to receive 1000 microg vitamin B-12, 1000 microg vitamin B-12 + 400 microg folic acid, or placebo for 24 wk. Vitamin B-12 status was assessed on the basis of methylmalonic acid, total homocysteine (tHcy), and holotranscobalamin (holoTC) concentrations before and after 12 and 24 wk of treatment. Cognitive function was assessed before and after 24 wk of treatment with the use of an extensive neuropsychologic test battery that included the domains of attention, construction, sensomotor speed, memory, and executive function.

RESULTS

Vitamin B-12 status did not change significantly after treatment in the placebo group; however, oral vitamin B-12 supplementation corrected mild vitamin B-12 deficiency. Vitamin B-12 + folic acid supplementation increased red blood cell folate concentrations and decreased tHcy concentrations by 36%. Improvement in memory function was greater in the placebo group than in the group who received vitamin B-12 alone (P = 0.0036). Neither supplementation with vitamin B-12 alone nor that in combination with folic acid was accompanied by any improvement in other cognitive domains.

CONCLUSION

Oral supplementation with vitamin B-12 alone or in combination with folic acid for 24 wk does not improve cognitive function.

Measurement of Total Vitamin B12 and Holotranscobalamin, Singly and in Combination, in Screening for Metabolic Vitamin B12 Deficiency

Background: The standard screening test for vitamin B12 deficiency, measurement of total plasma vitamin B12, has limitations of sensitivity and specificity. Plasma vitamin B12 bound to transcobalamin (holoTC) is the fraction of total vitamin B12 available for tissue uptake and therefore has been proposed as a potentially useful alternative indicator of vitamin B12 status.

Methods: We compared the diagnostic accuracy of total vitamin B12, holoTC, and a combination of both measures to screen for metabolic vitamin B12 deficiency in an elderly cohort (age ≥60 years). Plasma methylmalonic acid and homocysteine were used as indicators of vitamin B12 deficiency.

Results: Low total vitamin B12 (&lt;148 pmol/L) and low holoTC (&lt;35 pmol/L) were observed in 6.5% and 8.0%, and increased methylmalonic acid (&gt;350 nmol/L) and homocysteine (&gt;13 μmol/L) were observed in 12.1% and 17.0% of the study participants. In multiple regression models, holoTC explained 5%–6% more of the observed variance in methylmalonic acid and homocysteine than did total vitamin B12 (P ≤0.004). ROC curve analysis indicated that total vitamin B12 and holoTC were essentially equivalent in their ability to discriminate persons with and without vitamin B12 deficiency. Individuals with low concentrations of both total vitamin B12 and holoTC had significantly higher concentrations of methylmalonic acid and homocysteine than did individuals with total vitamin B12 and/or holoTC within the reference intervals (P &lt;0.001).

Conclusions: HoloTC and total vitamin B12 have equal diagnostic accuracy in screening for metabolic vitamin B12 deficiency. Measurement of both holoTC and total vitamin B12 provides a better screen for vitamin B12 deficiency than either assay alone.

The limited value of methylmalonic acid, homocysteine and holotranscobalamin in the diagnosis of early B12 deficiency

Treatment of B12 deficiency is important to prevent progressive neurological and/or hematologic disease but requires a secure diagnosis. The aim of this study was to evaluate second line tests of B12 status as prognostic indicators of a hematologic response to vitamin B12 therapy. Forty-nine patients referred with low, serum vitamin B12 concentrations were treated with intramuscular B12 and re-assessed after 3 months. Methylmalonic acid, homocysteine, holotranscobalamin and neutrophil hypersegmentation index were measured before and after treatment. Before treatment 27/49 patients were anemic or macrocytic of whom 15 had a clear hematologic response. All the tests had a similar prognostic accuracy. Symptomatic improvement did not correlate with hematologic response. Supplementary tests of vitamin B12 status were not significantly better than total serum B12 concentration as predictors of a hematologic response to vitamin B12 therapy.

Holotranscobalamin and Total Transcobalamin in Human Plasma: Determination, Determinants, and Reference Values in Healthy Adults

Background: We developed microbiological assays (MBAs) to identify determinants and to establish reference values for cobalamin bound to transcobalamin [holotranscobalamin (holoTC)] and total TC in plasma.

Methods: We captured holoTC with magnetic beads with TC antibodies and used a conventional MBA for cobalamin measurements. Total TC was determined as holoTC after TC was saturated with cyanocobalamin. The new assays were compared with published methods. Determinants and reference values were determined in 500 blood donors, ages 18–69 years.

Results: Determination of cobalamin, holoTC, and TC by MBA required &lt;150 μL. HoloTC and TC by MBA correlated with holoTC by RIA (r = 0.95) and TC by ELISA (r = 0.79), respectively. Between-day CVs for holoTC and total TC were 4%–9%. Women had lower holoTC than men, but only at age ≤45 years. In multivariate regression analyses, holoTC was positively associated with age (in women only), creatinine (in men only), and plasma concentrations of total TC, folate, and cysteine, but inversely correlated with homocysteine and methylmalonic acid. For all study participants, total TC was associated with holoTC and number of TCN2 766C alleles; in female participants only, total TC was also associated with age, homocysteine, and cysteine. Reference values were 670–1270 pmol/L for TC and 42–157 pmol/L for holoTC, but they differed according to age and sex.

Conclusions: Our MBAs for TC and holoTC required low plasma volume and performed acceptably compared with other methods. Determinants of holoTC and TC differed between men and women and according to age. Separate reference intervals for holoTC should be considered in younger women.

Study on serum transcobalamin II in patients with murine typhus

We measured the serum transcobalamin II in murine typhus- infected patients (n = 16) admitted to the Hospital for Tropical Diseases in 1996-1997, compared with healthy controls (n = 60). The results showed that the transcobalamin II (TCII) and total serum unsaturated vitaminB12 binding capacity (UBBC) in patients with murine typhus (2,126.5 pg/ml, range 1,262-4,568 and 3,771.5 pg/ml, range 1,576-6,763 pg/ml) were statistically significantly higher than normal subjects (987.5 pg/ml, range 678-2,000 pg/ml and 1,402 pg/ml, range 932-2,470 ml) (p<0.001). Serum TCII levels in patients (63%) were elevated during the febrile period and returned to normal post-treatment. These findings suggest that patients with murine typhus had stimulation of reticulo-endothelial system, spleen, mesenteric lymph nodes, liver and skin and then released TCII into the blood circulation. The elevation in TCII may be used for confirming a diagnosis of murine typhus.

Nonradioactive Vitamin B12 Absorption Test Evaluated in Controls and in Patients with Inherited Malabsorption of Vitamin B12

Background: Current tests for evaluation of vitamin B12 absorption are problematic because they involve the use of radioactively labeled vitamin B12. We describe a vitamin B12 absorption test that circumvents this problem.

Methods: We measured cobalamin or transcobalamin saturated with cobalamin (holo-TC) 24 h after three 9-μg doses of vitamin B12 given orally at 6-h intervals. We studied 17 patients with inherited malabsorption of vitamin B12 attributable to Imerslund–Grasbeck syndrome (n = 13) or intrinsic factor deficiency (n = 4), their obligate heterozygous biological parents (n = 19), and healthy controls (n = 44).

Results: In the patients, the median (range) change of holo-TC after the B12 load was not significant [1 (−42 to 5) pmol/L], nor was the change of cobalamin [−3 (−32 to 22) pmol/L], consistent with a lack of measurable active or passive absorption. In controls, however, the median (range) increases of holo-TC and cobalamin were 26 (−6 to 63) pmol/L and 41 (−37 to 109) pmol/L, respectively. Similarly, the parents showed increases of 23 (−2 to 47) pmol/L and 27 (−15 to 94) pmol/L. The mean areas under the ROC curves (95% confidence intervals) were 0.97 (0.93–1.0) for holo-TC and 0.87 (0.79–0.94) for cobalamin, distinguishing patients from controls. At a cutoff of 6 pmol/L for holo-TC, the diagnostic sensitivity (95% confidence interval) was 100 (81–100)%, and the diagnostic specificity was 92 (82–97)%.

Conclusion: Measurement of holo-TC after administration of vitamin B12 is a promising approach for evaluating vitamin B12 absorption.

Glycosylation independent measurement of the cobalamin binding protein haptocorrin

BACKGROUND

Haptocorrin carries the major part of the circulating vitamin B12. The protein is heavily glycosylated and this may have implications for its measurement.

METHODS

We used two different ELISA assays. In one assay, we employed antibodies against native HC and no pre-treatment of samples or calibrators. In the other assay, we used antibodies raised against deglycosylated HC, and deglycosylated the samples and calibrators by treatment with neuraminidase and PNGase prior to analysis. Plasma samples from healthy donors were analysed.

RESULTS

The ELISA against native HC showed a high detection limit (71 pmol/l) and a poor linearity for serial dilutions of samples. The ELISA against deglycosylated HC showed a detection limit of 1.6 pmol/l, an excellent linearity between 1.6 and 100 pmol/l (r(2) = 0.99) and an inaccuracy of 5% for concentrations ranging from 250 to 840 pmol/l. The 95% reference interval was 240-680 pmol/l (n = 148). The concentration of HC showed a strong association to plasma cobalamins (p < 0.0001).

CONCLUSIONS

An ELISA against native HC does not ensure an equimolar measurement of HC, while this is the case when a glycosylation independent assay is employed. Using this assay, a very strong correlation between total plasma HC and cobalamins in healthy donors is obtained.

Disturbed homocysteine and methionine cycle intermediates S-adenosylhomocysteine and S-adenosylmethionine are related to degree of renal insufficiency in type 2 diabetes

BACKGROUND

Diabetic nephropathy is a common complication in patients with type 2 diabetes that may increase atherothrombotic risk. Hyperhomocysteinemia (HHcy) further increases the risk in those patients. We studied concentrations of total homocysteine (tHcy) and its related metabolites S-adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy) in relation to B-vitamin status and renal function in patients with type 2 diabetes who developed diabetic nephropathy.

METHODS

The study included 93 patients with renal failure and type 2 diabetes. Chronic kidney disease was classified into four subgroups according to the National Kidney Foundation based on glomerular filtration rate plus pathologic abnormalities or markers of kidney damage.

RESULTS

Serum or plasma concentrations of the metabolites increased significantly with worsening of renal function, whereas serum concentrations of the B vitamins (folate, vitamins B12 and B6) did not differ appreciably between the groups. Moreover, plasma concentrations of AdoHcy and AdoMet were markedly increased in patients with kidney failure compared with those in stage 2 (median AdoHcy, 112.7 vs 10.5 nmol/L; median AdoMet, 162.0 vs 80.0 nmol/L). The AdoMet/AdoHcy ratio was more than 80% lower in patients with renal failure compared with stage 2. Vitamin B12 was a significant determinant of concentrations of AdoMet, tHcy, methylmalonic acid (MMA), and cystathionine.

CONCLUSIONS

Increased plasma concentrations of tHcy and methionine cycle intermediates (AdoMet, AdoHcy) are related to disturbed renal function in patients with type 2 diabetes. Vitamin B12 and/or folate are significant predictors of tHcy, cystathionine, MMA, and AdoMet. The effect of therapeutic doses of the B vitamins on AdoMet, AdoHcy, and their ratio should be tested in renal patients.

Holotranscobalamin--a first choice assay for diagnosing early vitamin B deficiency?

OBJECTIVES

The performance of holotranscobalamin (holoTC) was compared with the other markers of vitamin B12 deficiency, and the influence of age, renal function, and thyroid status was examined.

DESIGN AND INTERVENTIONS

We examined 937 individuals not treated with vitamin B12 but in whom vitamin B12 deficiency was suspected because of a plasma methylmalonic acid (MMA) above 0.28 micromol L(-1) within the past 4 years. Besides laboratory tests, a structured interview and a neurological examination were performed amongst 534 individuals. Amongst these, 140 individuals qualified for a randomized trial (MMA 0.40-2.00 micromol L(-1)). They were randomized to injections with vitamin B12 or placebo and re-examined after 3 months.

SETTING

One university hospital in Aarhus, Denmark.

RESULTS

The ROC curves indicate that holoTC (AUC: 0.90) compared favourable with plasma vitamin B12 (AUC: 0.85) for identifying individuals likely to have vitamin B12 deficiency (MMA > or =0.75 micromol L(-1) and plasma total homocysteine (tHcy) > or =15 micromol L(-1)), and further that holoTC (AUC: 0.91) might replace combined testing with plasma vitamin B12 and the metabolites. No association was observed between the biochemical markers and symptoms and signs possibly related to vitamin B12 deficiency. HoloTC, TC saturation, plasma vitamin B12, MMA, and tHcy were significantly associated with plasma creatinine (all with P <0.001). Only tHcy was significantly associated with thyroid stimulating hormone (P=0.02).

CONCLUSIONS

HoloTC shows promise as first-line tests for diagnosing early vitamin B12 deficiency.

The usefulness of holotranscobalamin in predicting vitamin B12 status in different clinical settings

Serum concentrations of homocysteine (Hcy) and methylmalonic acid (MMA) become increased in B12-deficient subjects and are therefore, considered specific markers of B12 deficiency. Serum level of holotranscobalamin (holoTC) becomes decreased before the development of the metabolic dysfunction. We investigated the usefulness of holoTC in diagnosing B12 deficiency in some clinical settings. We measured serum concentrations of holoTC, MMA, Hcy and total B12 in omnivores, vegetarians, elderly people and haemodialysis patients. Our results indicated that the incidence of holoTC <35 pmol/L was highest in the vegans (76%). Low holoTC and elevated MMA were detected in 64% of the vegans and 43% of the lacto- and lacto-ovovegetarians. An elevated MMA and a low holoTC were found in subjects with total serum B12 as high as 300 pmol/L. The distribution of holoTC in elderly people was similar to that in younger adults (median holoTC 55 pmol/L in both groups). A low holoTC and an elevated MMA were found in 16% of the elderly group. An elevated MMA and a normal holoTC were found in 20% of the elderly group who had a relatively high median serum concentration of creatinine (106.1 micromol/L). Serum concentrations of holoTC in dialysis patients were considerably higher than all other groups (median 100 pmol/L). This was also associated with severely increased serum levels of MMA (median 987 nmol/L). From these results it can be concluded that serum concentration of holoTC is a much better predictor of B12 status than total B12. This was particularly evident in case of dietary B12 deficiency. Serum concentrations of holoTC as well as MMA can be affected by renal dysfunction. Elevated MMA and normal holoTC in patients with renal insufficiency may not exclude vitamin B12 deficiency. HoloTC seems not to be a promising marker in predicting B12 status in renal patients.

Evaluation of the technical performance of novel holotranscobalamin (holoTC) assays in a multicenter European demonstration project

A commercially available holotranscobalamin (holo-TC) radioimmunoassay (RIA) (Axis-Shield, Dundee, Scotland) was evaluated in four laboratories and compared with a holoTC ELISA run in one laboratory. The performance of the holoTC RIA assay was comparable in three of the four participating laboratories. The results from these three laboratories, involving at least 20 initial runs of “low”, “medium” and “high” serum-based controls (mean holoTC concentrations 34, 60 and 110pmol/L, respectively) yielded an intra-laboratory imprecision of 6–10%. No systematic inter-laboratory deviations were observed on runs involving 72 patient samples (holoTC concentration range 10–160pmol/L). A fourth laboratory demonstrated higher assay imprecision for control samples and systematic deviation of results for the patient samples. Measurement of holoTC by ELISA showed an imprecision of 4–5%, and slightly higher mean values for the controls (mean holoTC concentrations 40, 70 and 114pmol/L, respectively). Comparable results were obtained for the patient samples. The long-term intra-laboratory imprecision was 12% for the holoTC RIA and 6% for the ELISA. In conclusion, it would be prudent to check the calibration and precision prior to starting to use these holoTC assays in research or clinical practice. The results obtained using the holoTC RIA were similar to those obtained using the holoTC ELISA assay.

Elevation of serum transcobalamin II in patients with scrub typhus

Serum transcobalamin II levels were measured in scrub typhus patients. Eighteen out of fifty-two patients admitted to Maharat Nakhon Ratchasima Hospital were diagnosed with scrub typhus infection. The serum unsaturated vitamin B12 binding protein (UBBC) and total vitamin B12 binding protein (TBBC) levels in these patients were significantly higher than in normal subjects (p < 0.001). The mean serum transcobalamin II level in the typhus patients was also significantly higher than in the normal subjects (p=0.004). There was a significant correlation between serum TCII levels and typhus IgM or IgG titers (p < 0.05), but not to total IgM levels. These findings indicate that patients with scrub typhus had stimulation of the recticuloendothelial system as a result of a considerable increase in transcobalamin II levels.

Clinical utility of serum holotranscobalamin as a marker of cobalamin status in elderly patients with neuropsychiatric symptoms

Early diagnosis of cobalamin deficiency is crucial, owing to the latent nature of this disorder and the resulting possible irreversible neurological damage. A normal serum cobalamin concentration does not reliably rule out a functional cobalamin deficiency and there does not at present seem to be any single diagnostic approach to achieve this diagnosis. A new marker for cobalamin status is the serum concentration of cobalamin bound to transcobalamin II (holoTC). Because methods suitable for routine use have been unavailable until recently, the clinical value of low holoTC is still uncertain. Furthermore, there is at the moment no gold standard or true reference method to diagnose subtle cobalamin deficiency, which makes evaluation of the clinical usefulness of holoTC and the estimation of sensitivity and specificity problematic. In this study, we aimed to assess whether low holoTC concentrations are congruent with other biochemical signs of cobalamin deficiency in a group of psychogeriatric patients. The findings in the present study show that holoTC is strongly related to serum cobalamin (0.68; p<0.001 in both patients and controls). Distribution of the different markers for cobalamin/folate status in the 33 patients with low levels of serum holoTC (below 40 pmol/l) showed that 17 patients had normal levels of the other markers for cobalamin status. This may indicate poor specificity of low holoTC for cobalamin deficiency. In 23 out of 176 patients with normal levels of holoTC we observed pathological levels of other markers for cobalamin deficiency. The use of holoTC in the present study group did not give significant additional information other than that given by serum cobalamin and therefore cannot be recommended in this clinical setting.

A Case of Postoperative Recurrence of Fibrolamellar Hepatocellular Carcinoma with Increased Vitamin B12 Binding Capacity in a Young Japanese Female

A 17-year-old Japanese female underwent major hepatic resection for a huge fibrolamellar hepatocellular carcinoma that was compressing the inferior vena cava. The tumor was not exposed at the surgical margin but was very close to it. A recurrent lesion at the surgical margin of the liver and a lymph node metastasis were discovered 9 months postoperatively together with a marked elevation of vitamin B12 binding capacity. These lesions were resected, and vitamin B12 binding capacity decreased thereafter. Peritoneal dissemination was detected by CT 16 months postoperatively, together with recurrent elevation of vitamin B12 binding capacity. Several types of chemotherapy, including intraperitoneal injection of epirubicin, were applied and improved the patient's quality of life somewhat, but the patient died of recurrent disease 34 months after the initial hepatic resection. This is the first report in Japan of fibrolamellar hepatocellular carcinoma with increased vitamin B12 binding capacity as a useful marker. Fibrolamellar hepatocellular carcinomas, if resected, have a better prognosis than ordinary hepatocellular carcinoma in Japan, as well as in Western countries. An aggressive strategy should be chosen, which consists mainly of precise surgical resection and postoperative multimodality therapy, including chemotherapy.

Holo-Transcobalamin Concentration and Transcobalamin Saturation Reflect Recent Vitamin B12 Absorption Better than Does Serum Vitamin B12

Background: We evaluated whether measurement of vitamin B12-saturated transcobalamin (holo-TC) concentrations or TC saturation (holo-TC:total TC) reflects active vitamin B12 absorption in healthy individuals and patients after vitamin B12 intake.

Methods: We obtained blood samples from 31 healthy individuals (age range, 25–57 years) before (days −1 and 0) and after (days 1, 2, and 6) oral administration of three 9-μg doses of vitamin B12. The blood samples from seven patients (age range, 22–39 years) suspected to have decreased vitamin B12 absorption were obtained before and 1 day after the vitamin B12 intake. The blood samples were analyzed for vitamin B12, total TC, and holo-TC. The TC saturation was calculated.

Results: Intraindividual variation was &lt;13% for all measured values, as calculated from samples removed on day −1 and 0. In healthy individuals (n = 31) after intake of vitamin B12, the maximum median (range) increase (as percentages and absolute values) was in TC saturation [52 (−2% to 128)% and 0.04 (0–0.23) as a fraction], closely followed by holo-TC concentrations [39 (0–108)% and 34 (0–149) pmol/L]. All but one healthy individual had an increase of ≥15% in these markers. Serum vitamin B12 showed a smaller increase [14 (−8 to 51)% and 36 (−27 to 290) pmol/L]. After vitamin B12 intake, three patients with Crohn disease had the lowest increases in holo-TC concentration (3, 7, and 14 pmol/L) and in TC saturation (0.004, 0.01, and 0.01) among patients and 30 healthy individuals.

Conclusion: Holo-TC concentrations and TC saturation reflect normal vitamin B12 absorption better than does serum vitamin B12.

Transcobalamin deficiency due to activation of an intra exonic cryptic splice site

Transcobalamin (TC), a vitamin B12 (cobalamin, Cbl) binding protein in plasma, promotes the cellular uptake of the vitamin by receptor-mediated endocytosis. Inherited TC deficiency is an autosomal recessive disorder characterized by megaloblastic anaemia caused by cellular vitamin B12 depletion. It may be accompanied by neurological complications, including a delay in psychomotor and mental development. This report describes three sisters with inherited TC deficiency resulting from a splicing defect in the TC gene. A point mutation was identified in intron 3 splice site of the TC gene that activates a cryptic splice site in exon 3. The transcript generated has an in-frame deletion of 81 nucleotides and the resulting truncated protein is unstable and not secreted by the cells. Until now, genetic studies have been reported in only five patients with TC deficiency and the molecular defect was different in each of them, which gives evidence for a genetic heterogeneity of the disease.

Low vitamin B-12 status in confirmed Alzheimer's disease as revealed by serum holotranscobalamin

OBJECTIVE

To examine the possible association of holotranscobalamin, the active fraction of serum cobalamin, with Alzheimer's disease.

METHODS

51 patients with pathologically confirmed Alzheimer's disease and 65 cognitively screened elderly controls were studied. Serum holotranscobalamin was measured by a new solid phase radioimmunoassay.

RESULTS

Geometric mean levels showed no significant case-control differences for serum total cobalamin, but lower levels of holotranscobalamin in Alzheimer's disease (41.1 pmol/l) than in controls (57.1 pmol/l) (p < 0.001). The odds ratio of Alzheimer's disease was significant for low holotranscobalamin but not for low total cobalamin.

CONCLUSIONS

Disturbed cobalamin status is common in Alzheimer's disease and accordingly measurement of holotranscobalamin should be considered in the assessment of cognitively impaired patients.

Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid concentrations, and hyperhomocysteinemia in vegetarians

BACKGROUND

Vegetarians have a lower intake of vitamin B-12 than do omnivores. Early and reliable diagnosis of vitamin B-12 deficiency is very important.

OBJECTIVE

The objective was to investigate vitamin B-12 status in vegetarians and nonvegetarians.

DESIGN

The study cohort included 66 lactovegetarians or lactoovovegetarians (LV-LOV group), 29 vegans, and 79 omnivores. Total vitamin B-12, methylmalonic acid, holotranscobalamin II, and total homocysteine concentrations were assayed in serum.

RESULTS

Of the 3 groups, the vegans had the lowest vitamin B-12 status. In subjects who did not consume vitamins, low holotranscobalamin II (< 35 pmol/L) was found in 11% of the omnivores, 77% of the LV-LOV group, and 92% of the vegans. Elevated methylmalonic acid (> 271 nmol/L) was found in 5% of the omnivores, 68% of the LV-LOV group, and 83% of the vegans. Hyperhomocysteinemia (> 12 micromol/L) was present in 16% of the omnivores, 38% of the LV-LOV group, and 67% of the vegans. The correlation between holotranscobalamin II and vitamin B-12 was weak in the low serum vitamin B-12 range (r = 0.403) and strong in the high serum vitamin B-12 range (r = 0.769). Holotranscobalamin II concentration was the main determinant of total homocysteine concentration in the vegetarians (beta = -0.237, P < 0.001). Vitamin B-12 deficiency led to hyperhomocysteinemia that was not probable in the upper folate range (> 42.0 nmol/L).

CONCLUSIONS

Vegan subjects and, to a lesser degree, subjects in the LV-LOV group had metabolic features indicating vitamin B-12 deficiency that led to a substantial increase in total homocysteine concentrations. Vitamin B-12 status should be monitored in vegetarians. Health aspects of vegetarianism should be considered in the light of possible damaging effects arising from vitamin B-12 deficiency and hyperhomocysteinemia.

RIA for serum holo-transcobalamin: method evaluation in the clinical laboratory and reference interval

BACKGROUND

Decreased serum holo-transcobalamin (holoTC) could be the earliest marker of cobalamin (Cbl) deficiency, but there has been no method suitable for routine use. We evaluated a new commercial holoTC RIA, determined reference values, and assessed holoTC concentrations in relation to other biochemical markers of Cbl deficiency.

METHODS

The reference population consisted of 303 individuals 22-88 years of age, without disease or medication affecting Cbl or homocysteine metabolism. In elderly individuals (>or=65 years), normal Cbl status was further confirmed by total homocysteine (tHcy; <19 micro mol/L) and methylmalonic acid (MMA; <0.28 micro mol/L) concentrations within established reference intervals. HoloTC in Cbl deficiency was studied in a population of 107 elderly individuals with normal renal function. The Cbl deficiency was graded as potential (total Cbl <or=150 pmol/L or tHcy >or=19 micro mol/L), possible (total Cbl <or=150 pmol/L and either tHcy >or=19 micro mol/L or MMA >or=0.45 micro mol/L), and probable (tHcy >or=19 micro mol/L and MMA >or=0.45 micro mol/L).

RESULTS

The intra- and between-assay imprecision (CV) for the holoTC RIA were 4-7% and 6-8%, respectively. A 95% central reference interval for serum holoTC was 37-171 pmol/L. All participants (n = 16) with probable Cbl deficiency, 86% of those with possible, and 30% of those with potential Cbl deficiency had holoTC below the reference limit (<37 pmol/L). The holoTC correlated with total Cbl (r(s) = 0.80; P <0.0001) and inversely with MMA (r(s) = -0.52; P <0.0001). HoloTC concentrations were significantly (P = 0.01) higher in women than in men.

CONCLUSIONS

The new holoTC RIA is precise and simple to perform. Low holoTC is found in individuals with biochemical signs of Cbl deficiency, but the sensitivity and specificity of low holoTC in diagnosis of Cbl deficiency need to be further evaluated.

High prevalence of cobalamin deficiency in Guatemalan schoolchildren: associations with low plasma holotranscobalamin II and elevated serum methylmalonic acid and plasma homocysteine concentrations

BACKGROUND

Studies conducted in Guatemala, Mexico, and Venezuela have found high prevalences of low plasma cobalamin (vitamin B-12) concentrations in infants and children. It is not known whether these low cobalamin concentrations are accompanied by altered metabolic functions.

OBJECTIVE

We sought to assess the prevalence of cobalamin deficiency in Guatemalan children by using sensitive and specific markers of deficiency.

DESIGN

Children (n = 553) were screened for low plasma cobalamin. Those with low plasma cobalamin (< 162 pmol/L) were matched by age, grade, and sex to those with marginal (162-221 pmol/L) and adequate (> 221 pmol/L) concentrations. In this matched subset (n = 180), additional biochemical indicators of cobalamin deficiency were measured.

RESULTS

Of the 553 children screened, 11% had low plasma cobalamin and an additional 22% had marginal concentrations. The prevalences of elevated serum methylmalonic acid (MMA), plasma homocysteine, or both were significantly higher in children with low and marginal plasma cobalamin than in children with adequate plasma cobalamin. Mean serum MMA was high in all groups compared with values reported in other populations. Mean plasma holotranscobalamin II concentrations were significantly lower in children with low rather than marginal or adequate plasma cobalamin. However, holotranscobalamin II was a less sensitive indicator of cobalamin depletion than was MMA.

CONCLUSION

Biochemical markers of cobalamin deficiency confirmed that the cobalamin status of children with low and marginal plasma cobalamin is inadequate to support normal metabolic function.

Holotranscobalamin as a Predictor of Vitamin B12 Status

We report on the performance of a new test, holotranscobalamin, as compared to well established markers of vitamin B12 deficiency (plasma cobalamins, methylmalonic acid, and homocysteine). Holotranscobalamin was analyzed in 143 samples by a competitive radiobinding assay (Axis-Shield). Employing a cut-off value of 50 pmol/l, holotranscobalamin showed a sensitivity of 1.00 and a specificity of 0.89 as regards discriminating between individuals with test results indicating vitamin B12 deficiency (methylmalonic acid > 0.70 micromol/l and plasma cobalamins < 200 pmol/l, n = 35) and individuals with test results inside the reference intervals (methylmalonic acid < 0.29 micromol/l and plasma cobalamins > or = 200 pmol/l, n = 35). In a group (n = 37) with low plasma cobalamins (< 200 pmol/l) and normal methylmalonic acid (< 0.29 micromol/l), 27 individuals had low holotranscobalamin, and in nine of these individuals plasma homocysteine supported the deficiency state (homocysteine > 15 micromol/l). Holotranscobalamin was low in 12 individuals with increased methylmalonic acid (> 0.40 micromol/l) and normal plasma cobalamins (> or = 200 pmol/l) (n = 36), and plasma homocysteine supported the deficiency state in four of these individuals. We conclude that holotranscobalamin is likely to be a sensitive marker of vitamin B12 deficiency that also has a reasonable specificity. Large-scale clinical studies are warranted in order to clarify the usefulness of holotranscobalamin in the clinical setting.

Functional Vitamin B12 Deficiency and Determination of Holotranscobalamin in Populations at Risk

BACKGROUND

The prevalence of a sub-clinical functional vitamin B12 deficiency in the general population is higher than previously expected. Total serum vitamin B12 may not reliably indicate vitamin B12 status. To get more specificity and sensitivity in diagnosing vitamin B12 deficiency, the concept of measuring holotranscobalamin II (holoTC), a sub-fraction of vitamin B12, has aroused great interest. HoloTC as a biologically active vitamin B12 fraction promotes a specific uptake of its vitamin B12 by all cells. In this study we investigated the diagnostic value of storage (holoTC) of vitamin B12 and functional markers (methylmalonic acid (MMA)) of vitamin B12 metabolism in populations who are at risk of vitamin B12 deficiency.

SUBJECTS AND METHODS

Our study included 93 omnivorous German controls, 111 German and Dutch vegetarian subjects, 122 Syrian apparently healthy subjects, 127 elderly Germans and finally 92 German pre-dialysis renal patients. Serum concentrations of homocysteine (Hcy) and MMA were measured by gas chromatography-mass spectrometry, folate and vitamin B12 by chemiluminescence immunoassay, and holoTC by utilizing a RIA test.

RESULTS

High Hcy (>12 micromol/l), high MMA (>271 nmol/l) resp. low holoTC (vitamin B12) in serum were detected in 15%, 8% resp. 13% (1%) of German controls, 36%, 60%, resp. 72% (30%) of vegetarians, 42%, 48% resp. 50% (6%) of Syrians, 75%, 42%, resp. 21% (7%) of elderly subjects and 75%, 67% resp. 4% (2%) of renal patients. The lowest median levels of holoTC were observed in vegetarians, followed by the Syrian subjects (23 and 35 pmol/l, respectively). Renal patients had significantly higher levels of holoTC compared to the German controls (74 vs. 54 pmol/l). In the vitamin B12 range between 156 pmol/l (conventional cut-off level) and 241 pmol/l, both mean concentrations of holoTC and MMA were in the pathological range. HoloTC was the earliest marker for vitamin B12 deficiency followed by MMA. Vitamin B12 deficiency causes folate trapping. A higher folate level is required to keep Hcy normal. The relationship between MMA and holoTC seemed dependent on renal function. In renal patients with a glomerular filtration rate below 36 ml/min, a significantly lower mean level of MMA was detected within the highest tertile of holoTC concentration, compared to the lowest tertile. Thus, in renal patients, a higher serum concentration of circulating holoTC is required to deliver sufficient amounts of holoTC into the cells.

CONCLUSION

Our data support the concept that the measurement of holoTC and MMA provides a better index of cobalamin status than the measurement of total vitamin B12. HoloTC is the most sensitive marker, followed by MMA. The use of holoTC and MMA enables us to differentiate between storage depletion and functional vitamin B12 deficiency. Renal patients have a higher requirement of circulating holoTC. In renal dysfunction, holoTC cannot be used as a marker of vitamin B12 status.

Predictors of cobalamin deficiency in Guatemalan school children: diet, Helicobacter pylori, or bacterial overgrowth?

OBJECTIVES

The authors investigated whether low vitamin B12 intake, impaired gastric function, infection, and bacterial overgrowth were risk factors for the high prevalence of cobalamin deficiency observed in Guatemalan children.

METHODS

The plasma cobalamin concentration of 556 school children was measured and classified as low, marginal, or adequate. In 60 children from each of these three groups, concentrations of serum methylmalonic acid (MMA), plasma homocysteine, and plasma holotranscobalamin II were measured, and usual dietary B12 intake was estimated. Serum gastrin and pepsinogen I concentrations were measured, and and bacterial overgrowth were diagnosed using C-urea and C-xylose breath tests, respectively.

RESULTS

infection was present in 83% (144 of 174) of children, and bacterial overgrowth was found in 25% (28 of 113). Children with infection had higher serum gastrin and pepsinogen I. There were no significant differences among the plasma cobalamin groups in the prevalence of infection, bacterial overgrowth, serum gastrin, or pepsinogen I concentrations. However, there was a significant positive correlation between serum MMA and gastrin concentrations. The average daily consumption of dietary B12 was 5.5 +/- 5.2 microg/day, but intakes for 23% of children were <1.8 micro g/day. B12 intake from fortified snacks added an additional 0.3 +/- 0.2 microg/day. B12 intake was not significantly different among the plasma cobalamin groups, but it was significantly correlated with plasma cobalamin.

CONCLUSIONS

The specific cause of cobalamin deficiency in this population remains unclear, but these results suggest that low dietary B12 intake is a risk factor and alterations in gastric secretions may also play a role.