MICROBIOLOGICAL ASSAY OF FOLIC ACID ACTIVITY IN HUMAN SERUM

Vitamin B nutrition in the Nigerian tropical ataxic neuropathy

Assessment of nutritional status of vitamin B components by plasma or blood levels indicated riboflavin deficiency and possibly thiamine deficiency in Nigerian patients who suffered from tropical ataxic neuropathy and neurologically normal Nigerians who subsisted on predominant cassava diet. Serum levels of folate, niacin, pyridoxine and panthothenic acid were normal. Vitamin deficiencies probably are minor factors, if any, in the pathogenesis of tropical ataxic neuropathy in Nigerians.

Quality control in the microbiological serum folate assay

Low values obtained in the microbiological assay of serum folate are often due to the presence of antibiotics in the test serum. The assay has been modified to permit consistent recognition of the presence and extent of such contamination. Other assay variables have been investigated and a quality control system devised which rapidly identifies the presence of inconsistencies in any one assay batch. The system further allows for the reporting of some clinically useful results from an imperfect assay batch thus reducing the necessity for reassay of some test sera.

Effect of some anticonvulsant drugs on depletion of folate in rats on a vitamin B12-deficient diet

Rats fed on vitamin B12-deficient or vitamin B12-supplemented diets and treated with phenobarbitone by intraperitoneal injection for 5 d showed significant increases in the activity of glutamate formiminotransferase in liver. The only significant depletion in liver folate activity was in vitamin B12-supplemented rats that were starved for 48 h. When rats were given the same diets, with phenobarbitone and diphenylhydantoin added, for 12 weeks or more in two separate experiments, significant increases in transferase activity were found only in the livers of animals fed on the deficient diet. However, there was significant depletion of liver folate in animals taking the supplemented diet.

The effects of dietary histidine, methionine and homocystine on vitamin B12 and folate levels in rat liver

1. L-histidine (20 g/kg) added to vitamin B12-deficient and cyanocobalamin-supplemented diets based on soya-bean flour reduced the growth of rats given the vitamin B12-deficient diet but stimulated growth of rats given the cyanocobalamin-supplemented diet. Liver weight (g/kg body-weight)increased, but the protein content of the livers decreased, in rats given histidine supplements. The histidine was associated with significantly higher folate concentrations in the livers of cyanocobalamin-supplemented rats.

Diagnostic value of the serum folate assay

The diagnostic value of the serum folate assay has been assessed in 90 patients, each of whom had a macrocytic anaemia and a low serum vitamin B(12) level. Twenty-nine (32%) patients were found to have anaemia due primarily to folate deficiency. The cause of the low serum vitamin B(12) levels is uncertain in the 22 (25%) patients with normal or borderline vitamin B(12) absorption. The effect of folic acid therapy was studied in four of these patients, and in each case the serum vitamin B(12) rose slowly to a normal level. The serum folate was low in only four (7.5%) of the 54 patients with pernicious anaemia, and the levels rose to normal on treatment with vitamin B(12) alone. A high serum folate occurred in eight (15%) pernicious anaemia patients. A normal serum folate indicated the diagnosis of pernicious anaemia or megaloblastic anaemia following partial gastrectomy. However, a normal serum folate and a very low vitamin B(12) level was found in two patients with idiopathic steatorrhoea. It is concluded that the serum folate assay is a valuable routine test in patients who have a macrocytic anaemia and low serum vitamin B(12). A low folate level makes the diagnosis of pernicious anaemia unlikely and is a strong indication for full investigation of small intestinal function.

Megaloblastic anaemia of pregnancy: a clinical and laboratory study with particular reference to the total and labile serum folate levels

It has been shown that the incidence of megaloblastic anaemia in a group of 463 randomly selected pregnant women receiving iron was 12 times as high as in a control group of 235 pregnant women receiving iron and folic acid. The incidence of all types of anaemia in the women receiving iron alone was more than three times the incidence in those having iron and folic acid. Some women who were not anaemic or who had normoblastic anaemia had serum folate levels in the same range as the women with megaloblastic anaemia, but none of the women with megaloblastic anaemia had high serum folate levels. The labile fraction of the serum folate was no more reliable than the total serum folate as a diagnostic criterion of megaloblastic erythropoiesis in the individual case. The blood group distribution in the women with megaloblastic anaemia was the same as in the general population. Babies born to mothers with megaloblastic anaemia tended to be smaller than the rest, although there was no difference in the placental weights. The significance of these findings is discussed.

A haematological study of patients receiving long-term treatment with trimethoprim and sulphonamide

The haematological effects of long-term treatment for three months with a combination of trimethoprim and sulphamethoxazole were studied in 10 cases of chronic bronchitis. Trimethoprim selectively inhibits dihydrofolate reductase in bacteria but not in man. Only minor effects on folate metabolism were observed in nine cases, causing no clinical concern. Some degree of thrombocytopenia occurred in the tenth case which improved when folinic acid was given.

Normal folic acid metabolism in iron-deficient rats

1. Weanling rats were fed on an iron-deficient diet without added folic acid and litter-mate controls received the same diet supplemented with Fe. Groups of deficient and control animals were killed at intervals of up to 88 days and glutamate formiminotransferase activity in liver and folic acid activity in liver and serum were measured.

2. No differences were found between the results from the deficient and control animals, although the deficient diet produced marked falls in haemoglobin, packed cell volume and serum iron.

3. In a second experiment folic acid was added to the diets and twelve rats received the Fe-deficient diet and their litter-mates were fed on the Fe-supplemented diet for 91 days. No differences were found in the activity of glutamate formiminotransferase purified from the combined livers of the two groups.

Estimation of red cell folate activity

The conditions described by Hoffbrand, Newcombe, and Mollin (1966) for the estimation of red cell folate activity have been confirmed using a different method (Spray, 1964) of micro-biological assay with Lactobacillus casei. In 81 control subjects the levels of folate activity in the red cells were between 80 and 470 mmug/ml (mean 192), and in plasma between 2.1 and 13 mmug/ml (mean 4.9). In 16 patients with megaloblastic anaemia due to folic acid deficiency, the red cell folate level was between 3 and 74 mmug/ml (mean 32). In 15 of these patients the plasma level was between 0.1 and 1.0 mmug/ml; in the other patient it was 3.3 mmug/ml. Subnormal red cell levels were found in only eight out of 29 other patients whose plasma folate level was below 2.0 mmug/ml. In 26 patients with untreated pernicious anaemia, the red cell folate activity was between 44 and 280 mmug/ml (mean 129) and the plasma level was between 1.6 and 19 mmug/ml (mean 7.5).

A survey of vitamin B-12 deficiency in an elderly psychiatric population

For many years, cases of pernicious anaemia associated with mental symptoms have been described, and interest in these symptoms was renewed following the introduction of liver therapy (Richardson, 1929; Phillips, 1931). Interest later appeared to decline, so that MacDonald Holmes (1956), almost 20 years after the last important clinical review of the subject, could comment with justification that although the cerebral lesions of pernicious anaemia had been recognized for more than a century they were still much less familiar than the lesions which occurred in the spinal cord and peripheral nerves. Since then vitamin B12 deficiency as a cause of mental symptoms has given rise to increasing interest, and this is reflected in recent suggestions that serum vitamin B12 assays should be carried out routinely in psychiatric patients and might be more informative nowadays than the routine Wassermann reaction (Strachan and Henderson, 1965; Hunter and Matthews, 1965).

Measurement of intestinal absorption of 57-Co vitamin B-12 by serum counting

The results of the measurement of vitamin B(12) absorption by counting the radioactivity of 5 ml. serum obtained eight to 10 hours after the ingestion of an oral dose of 0.5 mug. vitamin B(12) labelled with 0.5 muc. (57)Co are compared with those obtained with the urinary excretion (Schilling) test. Inadequate urine collection and impaired renal function were responsible for low results in the Schilling test in four of the 12 control subjects, and an incomplete urine collection in four patients with pernicious anaemia could have led to doubt about the validity of the low result. The measurement of serum radioactivity for 1,000 seconds gave conclusive results, the range in the patients with malabsorption of vitamin B(12) being between 0 and 24 counts per minute, and in the control subjects and other patients with megaloblastic anaemia between 28 and 64 counts per minute. The highest serum radioactivity level in a patient with pernicious anaemia was 19 counts per minute. Serum counting is simpler than the Schilling test and may be done alone when the patient's renal function is known to be poor, when urine collection is expected to be unreliable, or when the flushing dose of vitamin B(12) should be avoided. Otherwise there is an advantage in doing both tests together for confirmation.

Aseptic addition method for Lactobacillus casei assay of folate activity in human serum

An ;aseptic addition' method is described for microbiological assay with Lactobacillis casei of folate activity in human serum. It has the following advantages over the previously reported ;standard' method. 1 The manipulations involved in the assay are halved, by deleting autoclaving of serum in buffers. 2 The use of 1 g.% ascorbate better preserves serum folates than the lower amounts of ascorbate which are the maximum quantities usable in the standard methods. 3 Only 0.3 ml. of serum is required (0.1 ml. for one sample; 0.2 ml. for its duplicate).