MICROBIOLOGICAL ASSAY OF FOLIC ACID ACTIVITY IN HUMAN SERUM

A method is described for the microbiological assay of folic acid activity in serum with Lactobacillus casei as test organism and a modified medium in which the organism gives a greater growth response than in media previously detailed. The results of experiments carried out to validate the use of this medium are shown. In 94 control subjects levels of folic acid activity in the serum ranged from 2. to 28 mmug./ml. (mean 7.8). The values in nine out of 10 patients with megaloblastic anaemia due to deficiency of folic acid were 1.0 mmug./ml. or less and one result was 2.0 mmug./ml. In six patients with megaloblastic anaemia associated with pregnancy the results ranged from 0.7 to 4.0 mmug./ml., and in untreated pernicious anaemia 28 out of 31 results were within or above the control range and three values were just below the lower limit of normal.

THE DIRECT ANTIGLOBULIN (COOMBS) TEST IN MEGALOBLASTIC ANAEMIA

Folic acid deficiency with the picture of a megaloblastic bone marrow may develop in haemolytic anaemia, and, on the other hand, both vitamin B(12) and folic acid deficiency may produce signs of haemolysis. As the correct interpretation of a positive antiglobulin reaction associated with megaloblastic erythropoiesis is particularly important, the effect of deficiency of vitamin B(12) and folic acid on the results of the test was investigated in 32 patients with vitamin B(12) or folic acid deficiency and a positive antiglobulin reaction was obtained in ten. There was no correlation between the result of the test and the degree of anaemia, and there was no significant difference between the incidence of positive results associated with deficiency of vitamin B(12) or folic acid. In determining the significance of a positive result, the time interval before agglutination occurs is sometimes of greater value than the strength of the reaction or the result of the gamma globulin neutralization test.

ESTIMATION OF SERUM L. CASEI ACTIVITY

Measurement of the serum Lactobacillus casei (;folic-acid') activity is widely used as an index of folic-acid deficiency. Present methods of assay result in recovery of about half the active material in normal serum. A modified method of assay is described which gives higher L. casei values and a clearer distinction between the sera of normal subjects and of patients with folic-acid deficiency.

THE URINARY EXCRETION AND TISSUE RETENTION OF CYANOCOBALAMIN BY SUBJECTS GIVEN REPEATED PARENTERAL DOSES

The urinary excretion of injected cyanocobalamin was studied in 30 previously untreated vitamin B(12)-deficient patients by measuring the urinary radioactivity after repeated injections of (58)Co vitamin B(12). The dose range used was 54 to 30,000 mug., each patient receiving the same dose at each injection. The results show that there is no constant trend to the excretion of greater or smaller proportions of the amount injected. It is also shown that there is a wide variation in the amounts excreted by each individual and between individual patients and that the capacity of the tissues to retain injected cyanocobalamin is very great, the amounts retained often being greatly in excess of the normal body stores. The excretion of radioactivity after parenteral infections of (58)Co vitamin B(12) was usually complete within 24 hours but exceptions to this were seen. The significance and value of the results is discussed.

PERNICIOUS ANAEMIA AUTOANTIBODY TO GASTRIC PARIETAL CELLS: IMMUNOFLUORESCENCE TEST WITH RAT STOMACH

Rat stomach provided an excellent substrate for immunofluorescence testing of gastric parietal cell autoantibodies in 65 human sera. The results of similar tests using human stomach corresponded closely in the 42 cases examined. The rat stomach had some advantage over human stomach in its ready availability in the fresh state, its occasional brighter staining reactions, and its avoidance of non-specific staining by the sandwich immunofluorescence technique.