INVESTIGATIONS INTO THE EUGLENA METHOD FOR THE ASSAY OF THE VITAMIN B12 IN SERUM

Biosynthesis of cobamides: Methods for the detection, analysis and production of cobamides and biosynthetic intermediates

Vitamin B₁₂, cobalamin, belongs to the broader cobamide family whose members are characterized by the presence of a cobalt-containing corrinoid ring. The ability to detect, isolate and characterize cobamides and their biosynthetic intermediates is an important prerequisite when attempting to study the synthesis of this remarkable group of compounds that play diverse roles across the three kingdoms of life. The synthesis of cobamides is restricted to only certain prokaryotes and their structural complexity entails an equally complex synthesis orchestrated through a multi-step biochemical pathway. In this chapter, we have outlined methods that we have found extremely helpful in the characterization of the biochemical pathway, including a plate microbiological assay, a corrinoid affinity extraction method, LCMS characterization and a multigene cloning strategy.

The transcriptome of Euglena gracilis reveals unexpected metabolic capabilities for carbohydrate and natural product biochemistry

Euglena gracilis is a highly complex alga belonging to the green plant line that shows characteristics of both plants and animals, while in evolutionary terms it is most closely related to the protozoan parasites Trypanosoma and Leishmania. This well-studied organism has long been known as a rich source of vitamins A, C and E, as well as amino acids that are essential for the human diet. Here we present de novo transcriptome sequencing and preliminary analysis, providing a basis for the molecular and functional genomics studies that will be required to direct metabolic engineering efforts aimed at enhancing the quality and quantity of high value products from E. gracilis. The transcriptome contains over 30,000 protein-encoding genes, supporting metabolic pathways for lipids, amino acids, carbohydrates and vitamins, along with capabilities for polyketide and non-ribosomal peptide biosynthesis. The metabolic and environmental robustness of Euglena is supported by a substantial capacity for responding to biotic and abiotic stress: it has the capacity to deploy three separate pathways for vitamin C (ascorbate) production, as well as producing vitamin E (α-tocopherol) and, in addition to glutathione, the redox-active thiols nor-trypanothione and ovothiol.

Highly reactive trans-cyclooctene tags with improved stability for Diels-Alder chemistry in living systems

One of the challenges of pretargeted radioimmunotherapy, which centers on the capture of a radiolabeled probe by a preinjected tumor-bound antibody, is the potential immunogenicity of biological capturing systems. A bioorthogonal chemical approach may circumvent this drawback, but effective in vivo chemistry in mice, larger animals, and eventually humans, requires very high reagent reactivity, sufficient stability, and retained selectivity. We report here that the reactivity of the fastest bioorthogonal reaction, the inverse-electron-demand-Diels-Alder cycloaddition between a tetrazine probe and a trans-cyclooctene-tagged antibody, can be increased 10-fold (k2 = 2.7 × 10(5) M(-1) s(-1)) via the trans-cyclooctene, approaching the speed of biological interactions, while also increasing its stability. This was enabled by the finding that the trans-cyclooctene tag is probably deactivated through isomerization to the unreactive cis-cyclooctene isomer by interactions with copper-containing proteins, and that increasing the steric hindrance on the tag can impede this process. Next, we found that the higher reactivity of axial vs equatorial linked TCO can be augmented by the choice of linker. The new, stabilized, and more reactive tag allowed for improved tumor-to-nontumor ratios in pretargeted tumor-bearing mice.

Laboratory testing for cobalamin deficiency in megaloblastic anemia

Cobalamin (vitamin B12) deficiency is a common cause of megaloblastic anemia in Western populations. Laboratory evaluation of megaloblastic anemia frequently includes the assessment of patient cobalamin and folate status. Current total serum cobalamin measurements are performed in the clinical laboratory with competitive binding luminescence assays, whose results may not always accurately reflect actual cobalamin stores. Surrogate markers of cobalamin deficiency such as methylmalonic acid and homocysteine have been utilized to improve diagnostic accuracy; however, the specificity of these tests by themselves is rather low. Measurement of the biologically active fraction of cobalamin, holotranscobalamin, has been proposed as a replacement for current total cobalamin assays. Although holotranscobalamin measurements appear to have slighter better sensitivity, the specificity of this assay remains to be determined. The relative merits and demerits of commonly available methods to assess cobalamin deficiency in patients with suspected megaloblastic anemia are discussed.

Malabsorption of vitamin B12 in dermatitis herpetiformis and its association with pernicious anaemia

Serum vitamin B12 concentrations were determined in 129 patients and a pentagastrin test performed in 116 patients with dermatitis herpetiformis (DH). Low serum vitamin B12 levels were found in 27 patients (21%) and achlorhydria in 30. Forty-two patients with achlorhydria and/or vitamin B12 deficiency were subjected to further haematological and gastrointestinal investigations. Functional or morphological involvement of the small intestine was seen in almost all patients with vitamin B12 deficiency but, in addition, atrophic gastritis resulting in defective secretion of intrinsic factor (pernicious anaemia) was found in 8 cases (7% of all DH patients). Thus, a low vitamin B12 level in DH patients should result in a careful gastrointestinal examination as both an atrophic gastritis and a coeliac-like enteropathy have further clinical implications.

Prevalence and haemopoietic effects of low serum vitamin B12 levels in geriatric medical patients

The clinical significance of low serum vitamin B12 levels in elderly people is controversial. We aimed to document the prevalence of a low serum vitamin B12 (< 175 pmol/l) in patients referred to a geriatric medical unit, and to determine whether haemopoiesis is commonly affected in elderly patients with low serum vitamin B12. We studied prospectively 472 consecutive referrals to a geriatric medical unit; fifty-six (13%) had a low serum vitamin B12 level, of whom nineteen (34%) of the fifty-six also had evidence of Fe deficiency (serum ferritin < 45 ng/ml). Low vitamin B12 was associated with a raised mean erythrocyte volume (MCV; mean 96.0 (SD 6.7) fl), compared with a control group (91.7 (SD 6.0) fl; P = 0.001). However, only thirteen (23%) of the fifty-six patients with a low vitamin B12 had an MCV > or = 100 fl. Mean haemoglobin (Hb) levels were not significantly reduced in those with a low vitamin B12. In a subsequent study the haematological response to intramuscular hydroxocobalamin was examined in thirty-four patients with a low serum vitamin B12. Treatment resulted in a significant fall in MCV and rise in Hb; these effects could be detected both in those patients with an initially normal full blood count (change in MCV -1.2 (SD 1.2); Hb +0.5 (SD 0.6); P < 0.01) and in those with macrocytosis and/or anaemia (-9.1 (SD 11.8); +0.8 (SD 1.2); P < 0.05). A low serum vitamin B12 is common in geriatric medical patients. This is usually associated with an upset in erythropoiesis, although the abnormalities are often subtle and may not be apparent on inspection of the full blood count. Elderly patients with serum vitamin B12 < 175 pmol/l should be assumed to have vitamin deficiency even if their full blood count is normal.

OBSERVATIONS ON VITAMIN B12 IN SERUM AND CEREBROSPINAL FLUID IN MULTIPLE SCLEROSIS

There are several claims that B(12) concentrations in serum and cerebrospinal fluid are grossly abnormal in multiple sclerosis, but results are conflicting. This paper reports measurements of these concentrations in 40 serum samples and 23 samples of lumbar cerebrospinal fluid from cases of multiple sclerosis, and in appropriate controls, using Euglena gracilis, z strain. The serum concentrations were found to be normal; the mean concentration in cerebrospinal fluid was slightly reduced, but all values were within the control range. In both control samples and samples from cases of multiple sclerosis, the B(12) concentration in lumbar cerebrospinal fluid was correlated with the concentration in serum. There was no correlation between B(12) concentration and total protein in cerebrospinal fluid.A number of estimations of serum B(12) were also made with Lactobacillus leichmannii, after extraction in the presence and absence of cyanide. These showed a difference between cases of multiple sclerosis and controls, one interpretation of which might be that the serum in multiple sclerosis contains an abnormally low concentration of hydroxocobalamin.

Anaemia and other haematological abnormalities in patients admitted to long-term care

We investigated the occurence and causes of anaemia and other haematological abnormalities in 142 elderly patients (43 men, 99 women; median age 79 and 80 years), admitted to long-term care. Healthy 81-year-old subjects (n = 220) were used as reference group. Anaemia according to the WHO definition was much more common in the studied population (41%) than in a representative sample of 81-year-old subjects (10%). Somatically fit patients were less often anaemic (30%) than those with somatic illness (68%). The main causes for anaemia were: chronic disease (14.9%), recent haemorrhage (7.8%), iron deficiency (5.7%); and often multifactorial. Secondary leuko- or thrombocytosis occurred in 14 and 23%, drug-induced thrombocytopenia in 2.8% of the patients. Anaemia and other haematological abnormalities seen in elderly patients hospitalized for long-term care are often secondary to chronic or acute disorders. However, they also occur in patients without severe somatic impairment and many of them are reversible. Such findings should therefore not be neglected, but properly investigated, and if possible treated.

Radioimmunoassay that measures serum vitamin B12

AIMS

To develop a specific radioimmunoassay for the routine determination of serum vitamin B12.

METHODS

Antisera were raised in rabbits by immunisation with the monocarboxylic acid derivative of cyanocobalamin coupled to human serum albumin. Antibody titres and affinities were determined and the antiserum giving the highest binding affinity constant, Ka, was used to develop the assay protocol. Donkey-anti-rabbit gamma globulin-coated magnetisable particles were used to separate the bound from free vitamin B12. The considerable cobalamin binding capacity of human serum was destroyed by autoclaving in acetate-cyanide buffer. Sixty samples were assayed by the radioimmunoassay (RIA) and the Lactobacillus leichmannii assay. Recovery and cross-reactivity experiments were performed.

RESULTS

Final rabbit antibody titres varied from 1/20,000 to 1/188,000. Scatchard plots did not correlate with the antibody titres. The Ka values varied from 2.6 to 6.7 x 10(10) litres/mol. For maximum sensitivity the highest Ka (titre 1/66,000) was chosen. A tracer concentration of 22 pmol/l, an antiserum dilution of 1/100,000, and a sample volume of 0.1 ml were used. At an antiserum dilution of 1 in 100,000 the cyanocobalamin binding of the rabbit serum was diluted out. The assay showed excellent correlation with the microbiological assay, with 100% recovery of added vitamin B12. Levels of cross-reactivity for dicyanide cobinamide and hydroxocobalamin were 9.8 and 8.1%, respectively.

CONCLUSIONS

The development of this immunoassay permits the measurement of serum vitamin B12 without important interference from cobalamin analogues, related corrinoids, and non-specific binders.

Microbiological assay for vitamin B12 performed in 96-well microtitre plates

A simplified microbiological assay for vitamin B12 estimation, completed on microtitre plates using a colistin sulphate resistant strain of Lactobacillus leichmannii (NCIB 12519), and cryopreserved cultures is described. The new assay correlated well with a more conventional "tube" assay and was not influenced by the presence of antibiotics in serum. Evaluation of assay performance showed excellent interassay and intra-assay precision with quantitative recovery of added cyanocobalamin over a wide range of additions (94.9%-102.1%). The advantages of short incubation time, easy reading, and minimal reagent costs make this assay an attractive option in the routine clinical laboratory and in research.

Low serum cobalamin levels in a population study of 70- and 75-year-old subjects. Gastrointestinal causes and hematological effects

We examined causes and hematological consequences of low serum cobalamin (vitamin B12) concentration in two representative population samples of 70-year-old (N = 293) and 75-year-old subjects (N = 486). Subjects with values below 130 pmol/liter (4.8% and 5.6%, respectively) were investigated with Schilling test, upper gastrointestinal endoscopy, determination of serum gastrin and group I pepsinogens, and bone marrow examination. Gastrointestinal abnormalities of etiologic significance were found in 26 of the 32 examined subjects: atrophy of the gastric body mucosa (N = 16, with pernicious anemia in six), partial gastrectomy (N = 6), and intestinal malabsorption (N = 4). Megaloblastic hematopoiesis was found in 10 individuals, four of whom had macrocytic anemia. Our results indicate that low serum cobalamin concentration in the elderly is usually a consequence of disease rather than of high age per se and that gastric mucosal atrophy is a major etiologic factor.

Haematological abnormalities in a 75-year-old population. Consequences for health-related reference intervals

A representative sample (n = 486) of a 75-year-old population was studied, and probands with defined laboratory aberrations were re-investigated. Anaemia was present in 6% of the men and 3% of the women; in 17/22 anaemic subjects a cause was found. The prevalence of plasma cobalamin concentrations less than 130 pmol/l was 6%, of iron deficiency approximately 6%. Divergences in white blood cell and platelet counts were rare. The observed haematological aberrations were almost always caused by disease. Reference intervals for haematological components were calculated in the total study group and two reference sample groups after exclusions based on anamnestic and/or laboratory screening criteria or anamnestic criteria and/or verified disease. The lower reference limits for B-Hb and P-B12 in a group obtained after exclusions based on anamnestic and screening data were considered to be minimum values for healthy subjects. The WHO criteria for anaemia were applicable.

Incidence and clinical significance of protein-bound vitamin B12 malabsorption

Patient records from January 1975 to December 1984 were analysed to assess the possible incidence of protein-bound vitamin B12 malabsorption. This condition is characterised by a low serum vitamin B12 level and a normal Schilling test but impaired absorption of vitamin B12 bound to protein. We found that 48 (25%) patients with a low serum cobalamin level unexplained by other causes had a normal Schilling test. Megaloblastic haemopoiesis was found in 25 of these. From this group, all 10 patients who had a test of protein-bound vitamin B12 absorption showed impaired absorption. Protein-bound vitamin B12 malabsorption may represent an early phase of pernicious anaemia when hypochlorhydria precedes intrinsic factor deficiency and should be tested for when the serum vitamin B12 level is decreased and the Schilling test is normal.

Sjögren's Syndrome Associated with Vitamin B(12) Deficiency

Three patients showing Sjögren's syndrome in association with macrocytic anemia due to vitamin B(12) deficiency are described. Antibodies to parietal cells, intrinsic factor and salivary protein were investigated; positive test results were obtained in different combinations. Addisonian pernicious anemia as well as vitamin B(12)-malabsorption because of anti-intrinsic factor antibodies in gastric juice and/or malabsorption due to changes in the intestinal wall induced by Sjögren's syndrome are possible etiological factors. A case of Sjögren's syndrome associated with positive anti-parietal cell antibodies and histaminerefractory achylia is also reported. The concurrence of these two diseases known to be associated with autoimmune responses suggests the possibility of similar pathogenesis.

British standard for human serum vitamin B12

Seven laboratories took part in a collaborative study of an ampouled preparation of normal serum labelled 81/563. Each laboratory calibrated the preparation in terms of pure cyanocobalamin by use of Euglena assay. The inclusion of pernicious anaemia serum in the study and additional tests for safety and stability indicated that 81/563 would be a suitable standard for diagnostic testing. In 1985 the National Biological Standards Board established the preparation as the British Standard for Human Serum Vitamin B12 and, with the agreement of participants in the study, assigned it a potency of 320 picograms per ampoule.

Guillain-Barré syndrome. A clinical electrophysiological and biochemical study

Fifty-six consecutive patients with Guillain-Barré syndrome representing 49% of all cases of peripheral neuropathy (except those due to diabetes mellitus and leprosy) admitted to the Postgraduate Institute of Medical Education and Research, Chandigarh over a period of three years were studied. All patients developed weakness of limbs within one day to three weeks. Attenuation of deep tendon jerks (98%) paresthesia (66%), cranial nerve involvement (41%) and antecedent infection (32%) were the common clinical features. The common patterns of motor weakness were predominantly proximal in all the four limbs (45%) or predominantly proximal in lower limbs along with distal muscles in upper limbs (29%). Electrodiagnostic studies revealed prolonged distal (motor) latency (82%), reduced motor nerve conduction velocity (74%), sensory nerve conduction abnormality (85%) and evidence of denervation (41%). Evoked motor response of median, ulnar, common peroneal and tibial nerves exhibited significant increase in duration and reduction in amplitude. The maximum incidence of electrophysiological abnormality occurred between four to 12 weeks after the onset of neurological symptoms. Four patients died and 11 showed poor recovery. Long intervals (greater than 3 weeks) between peak deficit and onset of recovery and coexistence of reduced motor nerve conduction velocity with evidence of denervation on EMG were found to be associated with poor recovery.

Haematological findings in chronic alcoholics after heavy drinking with special reference to haemolysis

Haematological abnormalities are frequently found in heavy-drinking chronic alcoholics, but anaemia is generally a rare complication. When present, haemolysis is considered to be one of the most common causes. However, little is known about mild haemolysis without anaemia. The present report on eighteen male chronic alcoholics with a recent heavy debauche but without signs of severe liver disease gave support for the occurrence of a reversible low-degree haemolysis without concomitant gross changes of the erythrocytes. Thus the bone marrow showed an increased erythropoiesis in the absence of iron deficiency and known blood losses. Further, increased reticulocyte counts and low levels of haemopexin were noted in the early abstinence. Finally, during the withdrawal phase haptoglobin and haemopexin increased concomitantly with diminishing values of unconjugated bilirubin. The most likely cause of the proposed diminished red cell survival before the withdrawal is supposed to be a reduced membrane stability.

Megaloblastic anaemia due to vitamin B12 deficiency caused by small intestinal bacterial overgrowth: possible role of vitamin B12 analogues

Megaloblastic anaemia due to bacterial overgrowth of the small intestine is due to vitamin B12 malabsorption. This report describes a patient with bacterial overgrowth of the small intestine who had megaloblastic anaemia and malabsorption of vitamin B12, but persistently normal levels of serum vitamin B12 and normal serum and red cell folate levels. However, there was evidence of vitamin B12 deficiency as shown by an abnormal deoxyuridine suppression test and by the response to treatment with physiological doses of vitamin B12. A relative increase in biologically inactive vitamin B12 analogues may be the explanation for the normal vitamin B12 level in this patient.

Toxicity of bone marrow in dentists exposed to nitrous oxide

The morphology of the bone marrow of 21 dentists who habitually used nitrous oxide in their surgeries was investigated. Exposure to nitrous oxide was measured with an atmospheric sampling device, and each dentist was invited to fill in a questionnaire giving details of medical history, diet, and intake of alcohol. During the trial a full neurological and haematological investigation was carried out and a bone marrow aspirate was examined both morphologically and by the deoxyuridine suppression test. Mean exposures to nitrous oxide ranged from 159 to 4600 parts per million. In all subjects serum vitamin B12 and folate concentrations were within normal limits. Abnormal results of deoxyuridine suppression tests were obtained in three of the 20 dentists tested; two of these three had abnormal white cells in their peripheral blood films. This study provides direct evidence that occupational exposure to nitrous oxide may cause depression of vitamin B12 activity resulting in measurable changes in bone marrow secondary to impaired synthesis of deoxyribonucleic acid.

Absorption of food cobalamins assessed by the double-isotope method in healthy volunteers and in patients with chronic diarrhoea

To make a food preparation containing radioactively labelled cobalamins, rabbits were given repeated injections with 57Co-labelled cyanocobalamin. The liver was removed, homogenized, and fried for 1 min or boiled for 30 min. Of the radioactivity in the fried homogenate 41.7% was recovered in the centrifuged supernatant compared with 50.8% in the boiled homogenate. The radioactivity in the supernatants had a molecular size close to that of free 57Co-labelled cyanocobalamin. Forty-two per cent of the radioactivity in the whole homogenate had been incorporated into 5-deoxyadenosyl-, 10% into methyl-, and 16.5% into hydroxy-cobalamin. To assess the validity of a double-isotope method for measuring the intestinal absorption of doses of the 57Co-labelled liver cobalamins, 51CrCl3 was used as a non-absorbable marker. In 14 healthy volunteers the correlation coefficient between the absorption measured by the double-isotope technique and the faecal excretion test was highly significant (r = 0.96, p less than 0.005), and there was only a small variation in the 57Co/51Cr ratio in successive stool collections. In 11 patients with chronic diarrhoea there was a significant correlation between the absorption measured by the double-isotope technique and the faecal excretion test (r = 0.92, p less than 0.005), but in some patients there was considerable variation in the 57Co/51Cr ratio in successive stool collections.

Role of S-adenosylmethionine in DNA synthesis and haemopoiesis

In man, exposure to nitrous oxide (N2O) can produce neurological damage and megaloblastic change in the bone marrow due to inactivation of vitamin B12. Methionine metabolism is interrelated with that of vitamin B12 and folate; the effect of methionine on the impaired DNA synthesis produced by N2O was therefore studied in 17 patients undergoing surgery. 14 were anaesthetised with 50% N2O in oxygen for 3-24 h. The remaining 3 had been exposed to N2O for less than 3 h. All patients developed megaloblastic bone marrow change except 2 of the latter patients whose bone marrows remained normoblastic. The bone marrow was studied biochemically using the deoxyuridine (dU) suppression test. The in vitro addition of small doses of methionine was as effective as vitamin B12 itself in correcting the defective DNA synthesis produced by N2O. It is suggested that N2O impairs methionine biosynthesis, methionine, in the form of S-adenosylmethionine (SAM), being required for DNA synthesis and the prevention of the development of megaloblastic anaemia in man.

Absent ileal uptake of IF-bound vitamin B12 in vivo in the Imerslund-Grasbeck syndrome (familial vitamin B12 malabsorption with proteinuria)

A Syrian family is described with three children who had inherited selective vitamin B12 malabsorption associated with proteinuria. (Imerslund-Grasbeck syndrome). Although inherited the defect was apparently not present at birth. A third child had less severe vitamin B12 malabsorption, was not vitamin B12 deficient and had no proteinuria. Studies on two of the affected children with subcellular fractionation of the uptake of radioactive vitamin B12 by ileal tissue in vivo indicate a defect in the ileal receptors for IF-bound vitamin B12. These findings are different from the single in vitro experiment on a patient with this condition that has been previously reported.

Plasma cobalamin-binding and serum cobalamin in patients with folate deficiency

Plasma unsaturated R-binder and transcobalamin 2 (TC 2) levels were measured in 62 patients with folate deficiency and compared with 80 control subjects and 52 patients with pernicious anaemia. An increase in unsaturated R-binder concentration was found in the majority of patients with folate deficiency and with PA. In folate deficiency, however, the unsaturated R-binder was often elevated whether the serum cobalamin (Cbl) was low or normal, more frequently when the serum Cbl was normal. Results of a separate in vivo study of plasma retention of injected 57Co cyanocobalamin were consistent with these findings. An elevated TC2 was found in a small number of patients with folate deficiency and with PA. The serum Cbl appears to the maintained at a normal level in some patients with folate deficiency by an increase in R-binder, which is caused by folate deficiency itself.

Conventional malabsorption tests: do they detect the adult patient with villous atrophy?

A total number of 134 patients with subtotal or partial villous atrophy, of whom 49 had dermatitis herpetiformis, were investigated with blood folate assay and xylose and lactose absorption tests. Faecal fat excretion was determined in 71 patients without dermatitis herpetiformis (coeliac group). A comparison was made between three patient groups, the patients with dermatitis herpetiformis and the coeliac patients studied in 1970-74 and 1975-79, respectively. From clinical and biochemical analyses of these patients we conclude that although a combination of the four malabsorption tests used here still detect a majority of coeliac patients, small intestinal biopsy may reveal villous atrophy also in patients without any laboratory evidence for malabsorption by these commonly used tests. In dermatitis herpetiformis, however, the sensitivity of the tests used was low; these malabsorption tests therefore have little diagnostic value in this category of patients.

Incidence and pathogenesis of acute megaloblastic bone-marrow change in patients receiving intensive care

The incidence and pathogenesis of acute megaloblastic bone-marrow change and of abnormalities in DNA synthesis, as assessed with the deoxyuridine(dU) suppression test, have been investigated in a prospective study of 70 seriously ill patients admitted to an intensive-care unit. On admission megaloblastic bone-marrow change was present in 22 patients, 18 of whom had been anaesthetised with nitrous oxide for 2-6 h during surgical procedures before admission. 16 of these 18 patients died, compared with 7 of 22 patients in whom haemopoiesis remained normoblastic despite receiving equivalent amounts of nitrous oxide. An abnormal dU-suppression test developed only in patients who had received nitrous oxide; on admission an abnormal dU-suppression test was found in 39 of the 42 patients tested who had been exposed to the anaesthetic. The abnormality produced in the dU-suppression test by nitrous oxide in patients admitted to the intensive-care unit was more severe and recovery was slower than the abnormality seen in patients undergoing cardiac-bypass surgery. During the recovery period from the effects of nitrous oxide the pattern of correction of the dU-suppression test changed from that of vitamin-B12 deficiency to folate deficiency.

Hepatic iron stores and markers of iron overload in alcoholics and patients with idiopathic hemochromatosis

Liver iron concentrations were determined in 60 alcoholics with liver disease of varying severity, 15 patients with untreated idiopathic hemochromatosis, and 16 control subjects with biliary tract disease. Mean liver iron concentrations (microgram/100 mg dry weight) were significantly greater in the alcoholics (156.4 +/- 7.8 (SEM); P less than 0.05) and in patients with idiopathic hemochromatosis (2094.5 +/- 230.7; P less than 0.01) than in control subjects (53.0 +/- 7.0). Liver iron concentrations of greater than 140 micrograms/100 were found in 17 alcoholics (29%) and in all 15 patients with idiopathic hemochromatosis. Liver iron concentrations greater than 1000 micrograms/100 mg were found in all patients with idiopathic hemochromatosis but in none of the alcoholics. In the alcoholics no relationship existed between liver iron concentrations and the amount of alcohol consumed daily, the length of the drinking history, the amount of beverage iron consumed daily, or the severity of the liver disease. Serum ferritin concentrations reflected iron stores in patients with hemochromatosis and in alcoholics with minimal liver disease. However, in alcoholics with significant liver disease serum ferritin concentrations did not reflect iron stores accurately, although with normal values iron overload is unlikely. Serum iron concentration and percentage saturation of total iron-binding capacity were of little value in assessing iron status in either alcoholics or patients with hemochromatosis. Measurement of the liver iron concentration clearly differentiates between alcoholics with significant siderosis and patients with idiopathic hemochromatosis.

Iron deficiency and anemia among Indian women in Fiji

In June 1979, 245 Hindu and 240 Moslem women of childbearing age (14-45 yr) living in a semi-rural area north of Lautoka were tested for anemia and for iron-deficiency. Ninety-six (39%) of the 245 Hindu women and 77 (32%) of the 240 Moslem women were anemic according to World Health Organization criteria. Most of the cases of anemia were due to iron-deficiency. The prevalence of anemia did not change significantly with advancing age or increasing parity. Hookworm ova were found on examination of a single specimen of feces in 27 (14%) of 195 Hindu and 50 (24%) of 209 Moslem women. The presence of hookworm did not correlate with anemia. The red cell folate level was less than 160 micrograms/l in 117 (24%) of 478 women and the serum vitamin B12 level was less than 100 ng/l in 47 (10%) of 476 women. Subnormal levels of these vitamins did not correlate with anemia. The serum ferritin was determined to assess tissue iron stores. Two-hundred-and-twenty-four (46%) of 484 Indian women tested had serum ferritin values of less than 10 microgram/l; 400 (83%) had ferritin values of less than 26 microgram/l. The high prevalence of iron deficiency appears to be due predominantly to dietary factors.

A study of the true competitive protein binding of current vitamin B12 radioassays

The use of purified intrinsic factor in vitamin B12 radioassays has greatly reduced the misdiagnosis of pernicious anaemia in recent years, but anomalies still occur. Observations made on current vitamin B12 radioassays suggest that many methods fail to convert all serum cobalamins to cyanocobalamin and thus are not true competitive protein binding assays. No KCN in the extraction buffer resulted in an average 30% reduction in the vitamin B12 level in normal sera. High concentrations of KCN caused a significant increase in the vitamin B12 level in serum from most vitamin B12 deficient patients. This increase could have caused a misdiagnosis in 7 of 12 patients studied. The specificity of (57Co) cyanocobalamin binding to both transcobalamin II (TCII) in a pool of normal sera and to intrinsic factor in a commercial kit binder reagent was 99%. We conclude that the KCN concentration in the extraction mixture should be between 2 and 5 mg/l.

Severe megaloblastic bone marrow change associated with unsuspected mild vitamin B12 deficiency

Two patients are reported who developed peripheral blood abnormalities and marked megaloblastic bone marrow change within eleven days of cardiac bypass surgery. The patients were shown to have unsuspected mild vitamin B12 deficiency due to Addisonian pernicious anaemia. The megaloblastic changes were presumed to be precipitated by the increased demand for erythrocytes and platelets after surgery.

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.

Macrocytosis in alcohol-related liver disease: its value for screening

The incidence of macrocytosis, defined as a mean corpuscular volume (MCV) of greater than 95 fl and large red cells on peripheral blood film, was determined in 303 alcoholics with liver disease (95 females: 208 males), 60 non-alcoholics with chronic liver disease (44 females: 16 males) and 35 control subjects (15 females: 20 males). Macrocytosis was found in 70.3% (213/303) of alcoholics with liver disease and in 23.3% (14/60) of non-alcoholics with liver disease, P less than 0.001. MCV values greater than 100 fl were seen in 49.5% (150/303) of alcoholics, but in only 3.3% (2/60) of non-alcoholics, P less than 0.001. Macrocytosis was more frequent in female, 86.3% (82/95) than in male alcoholics 63.0% (131/208), P less than 0.001. Serum folate values less than 3 microgram/l were found in 14.5% (44/303) of alcoholics and in 11.7% (7/60) of non-alcoholics. Low serum folate values were found in 18.3% (39/213) of alcoholics with macrocytosis and in 35.9% (28/78) of those with macrocytic anaemia. Twenty alcoholics with pre-cirrhotic liver disease were followed over three months. Macrocytosis was present in 85.0% (17/20) at the outset and in 40% (8/20) 3 months later. The changes in MCV were independent of alcohol intake and serum folate values. Macrocytosis is a useful diagnostic indicator of alcoholism. MCV values greater than 100 fl in patients with liver disease almost invariably indicate alcohol-related disease. In the short-term, changes in MCV are of little use in monitoring alcohol intake.

Validity of transcobalamin II-based radioassay for the determination of serum vitamin B12 concentrations

A valid radioassay for the estimation of serum vitamin B12 in the presence of naturally occurring vitamin B12 (= cobalamin) analogues can be operated if serum transcobalamin II (TC II) is used as the binding protein. Serum samples that gave diagnostically discrepant results when their vitamin B12 content was analysed (i) by a commercial radioassay known to be susceptible to interference from cobalamin analogues, and (ii) by microbiological assay, were further analysed by an alternative radioassay which uses the transcobalamins (principally TC II) of diluted normal serum as the assay binding protein. Concordance between the results from microbiological assay and the TC II-based radioassay was found in all cases. In an extended study over a three-year period, all routine serum samples sent for vitamin B12 analysis that had a vitamin B12 content of less than 320 ng/l by the TC II-based radioassay (reference range 200-850 ng/l) were reanalysed using an established microbiological method. Over 1000 samples were thus analysed. The data are presented to demonstrate the validity of the TC II-based radioassay results in this group of patients, serum samples from which are most likely to produce diagnostically erroneous vitamin B12 results when analysed by a radioassay that is less specific for cobalamins.

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.