Ralph Carmel

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

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

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

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

Cobalamin and Osteoblast-Specific Proteins

Cobalamin deficiency has well-known hematologic and neurologic effects, but little is known about its other effects. We therefore studied the effect of cobalamin on osteoblast-related proteins. We found that mean (+/- 1 SD) levels of skeletal alkaline phosphatase in the blood were lower in 12 cobalamin-deficient patients (3.89 +/- 2.19 units per liter) than in 5 nondeficient and 5 iron-deficient control subjects (7.55 +/- 3.99 units per liter). The degree of the megaloblastic anemia correlated with the reduction in skeletal alkaline phosphatase levels (r = 0.67, P less than 0.01). With cobalamin therapy, levels of skeletal alkaline phosphatase rose in 11 of the 12 cobalamin-deficient subjects but not in the controls. The cobalamin-deficient patients also had significantly lower osteocalcin levels than the control subjects (1.11 +/- 0.77 vs. 1.84 +/- 0.49 nmol per liter). During cobalamin therapy, these levels rose in the cobalamin-deficient patients but not in the controls. In contrast to the levels of osteoblast-related proteins, hepatic alkaline phosphatase levels were similar in the patients and controls and were usually unaffected by cobalamin therapy. In vitro studies of calvarial cells from chicken embryos showed that their alkaline phosphatase content was cobalamin-dependent, thus supporting our in vivo observations in humans. Our findings suggest that osteoblast activity depends on cobalamin and that bone metabolism is affected by cobalamin deficiency, but we do not yet know whether cobalamin deficiency produces clinically important bone disease.

Racial patterns in pernicious anemia. Early age at onset and increased frequency of intrinsic-factor antibody in black women.

Pernicious anemia affects primarily elderly northern Europeans, but may affect others more often than previously thought. Therefore, we analyzed the data from 156 documented cases: there were 73 patients of European origin, 52 black patients and 31 Latin-American patients. The mean age (+/- 1 S.D.) at presentation among black women, 53 +/- 16 years, was lower than that of all the others (P less than 0.001 in most comparisons), and seven of the 33 black women were less than 40 years old. In addition, 23 of the 24 black women tested had circulating antibody to intrinsic factor. A similar though less striking antibody prevalence (85 per cent) and age pattern (60 +/- 13 years) in Latin-American women did not reach statistical significance. No other group exceeded the usual 55 to 70 per cent prevalence of antibody. These finding suggest a different form of or a different response to the disease in black women and perhaps in Latin-American women.

Hereditary Defect of Cobalamin Metabolism (CblG Mutation) Presenting as a Neurologic Disorder in Adulthood

AN increasing variety of hereditary disorders of intracellular cobalamin metabolism, usually first detected because of the presence of methylmalonic aciduria (cblA, cblB, and cblF mutations), homoc...

Mild Transcobalamin I (Haptocorrin) Deficiency and Low Serum Cobalamin Concentrations

BACKGROUNDnLow cobalamin concentrations are common, but their causes are often unknown. Transcobalamin I/haptocorrin (TC I/HC) deficiency, viewed as a rare cause, has not been examined systematically in patients with unexplained low serum cobalamin.nnnMETHODSnTotal TC I/HC was measured by RIA in three subgroups of 367, 160, and 38 patients with different categories of low cobalamin concentrations and three comparison subgroups of 112, 281, and 119 individuals with cobalamin concentrations within the reference interval. Additional studies, including family studies, were done in selected patients found to have low TC I/HC concentrations.nnnRESULTSnLow TC I/HC concentrations suggestive of mild TC I/HC deficiency occurred in 54 of 367 (15%) patients with low cobalamin identified by clinical laboratories and 24 of 160 (15%) patients whose low cobalamin was unexplained after absorption and metabolic evaluation, but in only 2 of 38 patients with malabsorptive causes of low cobalamin concentrations (5%). The prevalence was only 3% (8 of 281 plasma samples) to 5% (6 of 112 sera) in patients with cobalamin concentrations within the reference interval and 3% (4 of 119) in healthy volunteers. Three patients with low cobalamin (0.6%) had severe TC I/HC deficiency with undetectable TC I/HC. Presumptive heterozygotes for severe TC I/HC deficiency in two families had the findings of mild TC I/HC deficiency; mild deficiency was also found in at least three of seven studied families of patients with mild TC I/HC deficiency.nnnCONCLUSIONSnMild TC I/HC deficiency is frequently associated with low cobalamin, is often familial, and its biochemical phenotype appears identical to the heterozygous state of severe TC I/HC deficiency. Severe TC I/HC deficiency also appears to be more common than suspected. Both diagnoses should be considered in all patients with unexplained low serum cobalamin.

Biomarkers of folate status in NHANES: a roundtable summary

A roundtable to discuss the measurement of folate status biomarkers in NHANES took place in July 2010. NHANES has measured serum folate since 1974 and red blood cell (RBC) folate since 1978 with the use of several different measurement procedures. Data on serum 5-methyltetrahydrofolate (5MTHF) and folic acid (FA) concentrations in persons aged ≥60 y are available in NHANES 1999–2002. The roundtable reviewed data that showed that folate concentrations from the Bio-Rad Quantaphase II procedure (Bio-Rad Laboratories, Hercules, CA; used in NHANES 1991–1994 and NHANES 1999–2006) were, on average, 29% lower for serum and 45% lower for RBC than were those from the microbiological assay (MA), which was used in NHANES 2007–2010. Roundtable experts agreed that these differences required a data adjustment for time-trend analyses. The roundtable reviewed the possible use of an isotope-dilution liquid chromatography–tandem mass spectrometry (LC-MS/MS) measurement procedure for future NHANES and agreed that the close agreement between the MA and LC-MS/MS results for serum folate supported conversion to the LC-MS/MS procedure. However, for RBC folate, the MA gave 25% higher concentrations than did the LC-MS/MS procedure. The roundtable agreed that the use of the LC-MS/MS procedure to measure RBC folate is premature at this time. The roundtable reviewed the reference materials available or under development at the National Institute of Standards and Technology and recognized the challenges related to, and the scientific need for, these materials. They noted the need for a commutability study for the available reference materials for serum 5MTHF and FA.

Monitoring of vitamin B-12 nutritional status in the United States by using plasma methylmalonic acid and serum vitamin B-12

BACKGROUNDnVarious definitions, criteria, tests, and cutoffs have been used to define vitamin B-12 status; however, a need exists for the systematic study of vitamin B-12 status in the United States because of concerns about high folic acid intakes and the potential for associated adverse effects.nnnOBJECTIVEnThe objective was to determine the effect of different cutoff choices on outcomes and of the different degrees of serum vitamin B-12 status, definable by the concurrent use of a functional and circulating marker as the first steps to developing a data-based consensus on the biochemical diagnosis of vitamin B-12 deficiency.nnnDESIGNnData from NHANES, a nationally representative cross-sectional survey, were examined for adults aged >19 y (mean ± SD age: 45 ± 1 y) from 1999 to 2004 (n = 12,612).nnnRESULTSnCommonly used cutoffs had a greater effect on prevalence estimates of low vitamin B-12 status with the use of vitamin B-12 than with the use of methylmalonic acid (MMA; 3-26% and 2-6%, respectively). A cutoff of >148 pmol/L for vitamin B-12 and of ≤210 nmol/L for MMA resulted in significant misclassifications. Approximately 1% of adults had a clear vitamin B-12 deficiency (low vitamin B-12 and elevated MMA); 92% of adults had adequate vitamin B-12 status. A high percentage of younger women characterized the group with low vitamin B-12 and normal MMA (2% of adults) and may have falsely reflected low vitamin B-12. Adults with elevated MMA (5%) only were demographically similar (ie, by age and race) to the deficient group and may have included some individuals with early vitamin B-12 deficiency.nnnCONCLUSIONSnThese analyses indicate the challenges of assessing vitamin B-12 status when uncertainties exist about the appropriate cutoffs. Future studies should determine definable endpoints to achieve this goal.

Failures of cobalamin assays in pernicious anemia.

The authors show that commercial tests for cobalamin levels provide false normal values in 22 to 35% of cases of pernicious anemia, the main disease they were designed to detect. The manufacturers need to solve the problem of interference of the assay by antibodies to intrinsic factor.

Extreme Elevation of Serum Transcobalamin I in Patients with Metastatic Cancer

Elevation of transcobalamin I and serum vitamin B12 levels has usually been associated with increased granulocytic proliferation, such as occurs in chronic myelogenous leukemia. Two patients with metastatic cancer had extremely high serum vitamin B12 and transcobalamin I levels--greater than those seen in even the most intense granulocytic proliferation--that were not explainable by leukocytosis. The subjects serum vitamin B12 levels were 18,750 and 21,221 pg per milliliter (normal, 471 plus or minus 174 pg per milliliter, mean plus or minus S.D.) and unsaturated vitamin B12 binding capacity 158,750 and 5,400 pg per milliliter (normal, 1153 plus or minus 313 pg per milliliter) respectively. The abnormally elevated serum binder was shown to be identical with transcobalamin balamin I in every respect. Levels of transcobalamin II and serum third binder were normal. The cause of the binder abnormality is unknown, but factors other than granulocyte proliferation may control or contribute to the production or accumulation of transcobalamin I.