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

Chronic maternal methanol inhalation in nonhuman primates (Macaca fascicularis): exposure and toxicokinetics prior to and during pregnancy

Toxicokinetic studies were conducted following daily inhalation exposure to methanol vapor prior to and throughout pregnancy in adult female Macaca fascicularis monkeys. They were part of a larger study to investigate the effects of chronic methanol exposure on maternal reproductive performance and early offspring effects. In a two-cohort study design, 48 females (24/cohort) were assigned to parallel exposure groups at 0 (control), 200, 600, or 1800 ppm methanol vapor for approximately 2.5 h/day, 7 days/week throughout breeding and pregnancy. Blood methanol at 30 min postexposure was monitored biweekly. The time course for the clearance of blood MeOH concentrations following exposure was characterized on four occasions: twice during the prebreeding period and during mid- and late pregnancy. Average blood methanol concentrations at 30 min postexposure were 5, 11, and 35 microg/ml across all four toxicokinetic studies in the 200, 600 and 1800 ppm groups, respectively. Blood concentrations in the 200 ppm group were barely above basal (preexposure) blood methanol concentrations or those observed in the control group (approximately 3 microg/ml). Nonlinear elimination kinetics were observed in most of the 1800 ppm group females. There was a decrease in elimination half-life (7-20%) and an increase in clearance (30%) after 3-months of daily MeOH exposure compared to the initial exposure. There were no statistically significant changes in the first-order blood methanol half-life or clearance during pregnancy, but the mean distribution volume per kilogram body weight decreased by 22% and 17% in the 600 and 1800 ppm groups. Plasma formate levels did not differ between the methanol and control exposure groups. Plasma formate and serum folate concentrations increased slightly over the course of this study in both the exposed and control groups but these increases were not related to methanol exposure.

Iron Deficiency Developing in Patients with Homozygous Hypercholesterolaemia on Long-term Plasmapheresis is Significantly Contributed to by Extracorporeal Haemolysis

Patients with homozygous hypeicholesterolaemia are notoriously refractory to pharmacologic intervention, leaving regular long-term plasmapheresis as one of the most effective forms of therapy. In this situation we noted the universal development of anaemia; accordingly, its pathogenesis was investigated in a stable cohort of patients over a two year period. Radionuclide studies were carried out in 8 of the 9 available individuals: of these 3 who were not on treatment and 3 out of 5 on the apheresis programme had mean red cell lifespan below the lower level of our normal range. The creation of an arterio-venous fistula and subsequent performance of plasma exchange procedures every two weeks was followed by a falling haemoglobin concentration and the appearance of hypochromasia and microcytosis. The latter was the result of substantial loss of iron through venesection, in the discard plasma and by a transient peak of the iron in the urine: the last two compartments were studied using inductively coupled plasma atomic emission spectrometry (ICP-AES). Such depletion could not be compensated for by a dietary intake of iron that barely met the recommended daily allowance whereas the anaemia reversed readily on oral supplementation. This is the first report of extracorporeal haemolysis in this clinical setting and recognition of its pathophysiology directly influences management. Thus, oral iron supplementation should prevent anaemia and its symptoms whilst also circumventing the paradoxical hyperviscosity that might otherwise occur from iron deficiency.

Homocysteine increases as folate decreases in plasma of healthy men during short-term dietary folate and methyl group restriction

Ten healthy adult men were fed a diet low in folate and exogenous methyl groups to study the effects on folate requirement and status. The men were housed in a metabolic unit for the entire 108-d study. After a 9-d base-line period (P1), the men were fed an amino acid-defined soybean product diet for 45 d, which provided 25 micrograms/d of folate for 30 d (P2) and (with a folate supplement) 99 micrograms/d for 15 d (P3). During P2 and P3, the low methionine and choline diet was supplemented with methionine for half the subjects to vary the dietary methyl group intake. The periods were then repeated over the next 54 d (P4-P6), with a cross-over of methionine intakes in P5 and P6. Restricting dietary methyl group intake did not increase the dietary folate requirement. Plasma total homocysteine rose during folate depletion and correlated inversely with plasma folate; however, the response of homocysteine to changes in folate intake varied among individuals from very strong to absent. The results support previous suggestions that increased plasma homocysteine concentrations provide a marker of functional folate deficiency, and further indicate that individuals may differ greatly in their susceptibility to hyperhomocysteinemia due to low folate intakes. Judged by the lack of normalization of high homocysteine concentrations during folate repletion, the current folate RDA for adult men may not provide the expected margin of protection.

Erythrocyte folate levels: a clinical study

PURPOSE

1) To determine if there are significant differences in laboratory parameters and patient characteristics between patients with low erythrocyte (RBC) folate levels and those with normal RBC folate levels; 2) to determine the correlation between serum and RBC folate levels; 3) to determine if the RBC folate level changed the diagnosis, treatment, and outcome of these patients if the serum folate level was available.

PATIENTS AND METHODS

The study is a retrospective review of all inpatients and outpatients at a public teaching hospital who had an RBC folate level less than or equal to 175 ng/ml (N = 57) over the study period (69 months) and a blindly selected group of patients with RBC folate levels greater than 175 ng/ml (N = 53) during the same period.

RESULTS

Patients with low RBC folate levels had higher mean corpuscular volume (MCV) and red cell distribution width (RDW) values and lower serum folate and B12 values than patients with normal RBC folate levels, but there was no difference in degree of anemia, presence of oval macrocytes and/or hypersegmented neutrophils on the peripheral blood smear, LDH, alcohol use, diet, or any other measured clinical parameter. Serum and RBC folate levels were highly correlated and a low RBC folate affected the clinical outcome of three patients (5% of the low RBC folate group).

CONCLUSIONS

Based upon these retrospective data and a review of the literature, we cannot define significant differences between patients with low RBC folate and randomly selected patients with normal RBC folate that could not have been equally well defined using serum folate values. The sensitivity and specificity of a low RBC folate level in the diagnosis of ill or healthy individuals are undefined, and until prospective studies utilizing some of the newer, more specific biochemical indicators of tissue folate are completed, the interpretation of low RBC folate levels will remain problematic.

A Comparison of Commercial Kit Methods for Assay of Vitamin B12in Ruminant Blood

Five commercially available radioisotope dilution (RID) kits for assay of Vitamin B(12) were obtained for evaluation with ovine and bovine serum; also, for comparison with our laboratory's (Lab 1) RID method and the methods of two independent laboratories, one using RID and the other a microbiological method. One commercial kit was found to be suitable for both species because negligible non-specific binding occurred when extraction was performed at 100 degrees C (212 degrees F). Of the other four kits, two were found to be suitable for ovine and bovine serum provided non-specific binding of the latter was measured. This was also the case with the Lab 1 method. Two of the commercial kits were found to be unsuitable for assay of Vitamin B(12)in ruminant blood.

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.

Evaluation of a commercial radioassay for the simultaneous estimation of vitamin B12 and folate, with subsequent derivation of the normal reference range

A commercial assay kit method for the simultaneous estimation of vitamin B12 and folate concentrations has been evaluated. Values derived for folate by a microbiological assay and vitamin B12 by a verified radioassay showed good correlation with the investigated method. The clinical sensitivity of the assay for detecting deficient concentrations of vitamin B12 and folate was comparable to that of the non-commercial methods and other more definitive clinical procedures. Establishment of reference ranges, based on accepted statistical criteria, are discussed and such ranges are contrasted with those proposed by the manufacturer. The kit method is time and labour saving compared with the non-commercial methods.

Comparison of methods used in commercial kits for the assay of serum vitamin B12

Fourteen commercial kits for serum vitamin B12 assay have been assessed. The analytical performance and clinical correlation were used to rank the methods employed for the extraction of the vitamin from its binders and for the separation of 'bound' from 'unbound' counts. The introduction of extraction without boiling and the separation by attachment of the vitamin B12 binder to a solid matrix have not been shown to be generally better or worse than conventional methods.

The need for a sufficient number of low level sera in comparisons of different serum vitamin B12 assays

Eight radiochemical methods for the assay of vitamin B12 in serum were compared with the microbiological assay with Lactobacillus leichmannii ATCC 7830 using 198 individual sera of patients. There was a good agreement between the results of most samples with some kits and the microbiological assay. However, especially in the sera of vitamin B12-deficient patients large discrepancies between the results could occur. These variations were due to both the kits used and the performance of the assays in different laboratories. A sufficient number of non-pooled sera of vitamin B12-deficient patients should be included in investigations to validate radiochemical methods.

Folate assays--an alternative to microbiological assays and commercial kits

A simple and reliable folate radioassay technique based on the principles of classic folate radioassays but incorporating several of the recently introduced technical innovations is presented as an alternative to the microbiological assays and commercial kits. Serum and red cell folate values from this method were compared with results from two commercial kits and a Lactobacillus casei (L. casei) assay. There was a good correlation with the L. casei assay for both serum and red cell folate (r = 0.95). The method uses N-methyltetrahydrofolate standards diluted in folate free serum, beta-lactoglobulin as a binder and an alkaline denaturation ('no-boil') of endogenous folate binding proteins. Low hematocrit lysates were best performed at a 1 in 10 rather than 1 in 20 dilution. A comparison of the boil and 'no-boil' kits from Diagnostic Products Corporation revealed that the 'no-boil' kit produced results closer to those obtained from the L. casei assay than the boil kit.

Hematologic disorders in the elderly

Management of hematologic disorders in older patients must often be weighed in a setting of decreased physiological reserves and concurrent illnesses. Anemia in the elderly should never be attributed to old age. Even a mild anemia in collusion with multiple physical and mental problems may tip the balance for those previously able to cope with their disabilities. Iron deficiency anemia and the anemia of chronic disease are the most common types of anemia in the elderly. Nutritional anemias due to folate or vitamin B(12) deficiency are treatable and should not be overlooked. Newer chemotherapy regimens for acute nonlymphocytic leukemia have been effective in many older patients. Decisions to treat are sometimes difficult, often depending on the aggregate of coexistent physical and mental disorders. The most prevalent type of leukemia in the elderly is chronic lymphocytic leukemia. A benign asymptomatic course requires no therapy, but aggressive disease requires treatment. Multiple myeloma should be suspected in an elderly person who has both unexplained anemia and bone pain. After definitive diagnosis, phlebotomy therapy should be considered for both polycythemia vera and secondary erythrocytosis to reduce blood viscosity and increase cerebral blood flow.

Comparative studies of a new commercial kit for the estimation of vitamin B12 in serum

A commercial kit method (Technia Diagnostics) for the estimation of serum vitamin B12 claiming certain practical advantages was examined. Analytical and clinical performance were compared with a non-commercial radioisotope B12 method, previously compared to other commercial radioisotope B12 methods. The kit's analytical performance in our hands was satisfactory, although the within-batch precision and recovery of added cyanocobalamin were disappointing. Clinical performance was comparable with the non-commercial B12 method. Establishment of suitable reference ranges as a prerequisite to diagnostic use is apparent.