Method of assay of red cell folate activity and the value of the assay as a test for folate deficiency

Abstract

SYNOPSIS A simplified microbiological assay for determining the folate content of red cells is described. As in previously reported methods Lactobacillus casei is used as test organism but two modifications are introduced. First, haemolysis is carried out in water containing 1 g. % of ascorbic acid; secondly, haemolysates are not incubated before the assay. Using this assay, recovery of pteroylglutamic acid added in two different concentrations to five different whole blood samples was 97 0 ± 1l9 S.E. % and 106 1 ± 4i7 S.E. % respectively. The coefficient of variation of the assay was between 11-2 and 15-0%.Haemolysates were best stored deep frozen, showing no significant loss of L. casei activity for three to five months at -20°C. On the other hand, non-haemolysed blood samples were best stored at 40C. when there was no loss of activity for seven to 10 days.Experiments confirmed that plasma is necessary for the maximum release of red cell L. casei activity, and showed that only small amounts of plasma are necessary; folate-and B12-deficient plasma released slightly lower L. casei activities from red cells than did normal plasma. The red cell folate levels of 40 healthy normal subjects ranged from 160 to 640 m,ug. per ml. of packed red cells. One hundred and twenty patients with subnormal serum folate levels due to idiopathic steatorrhoea, nutritional folate deficiency and Crohn's disease, partial gastrectomy, myelosclerosis, and polycythaemia vera were studied. Red cell folate levels were subnormal (range from 7 to 143 m,ug. per ml.) in 40 patients with megaloblastic anaemia, the lowest levels occurring in the most anaemic patients. Subnormal red cell folate levels also occurred in 23 (29 %) of the 80 nonanaemic patients. There was a good correlation between red cell folate level and severity of folate deficiency assessed by polymorph nuclear lobe counts, and, in the non-anaemic patients bone marrow morphology. It is concluded that, in the absence of B12 deficiency, the red cell folate level is a precise guide to the severity of folate deficiency.Patients with serum folate levels less than 3-0 m,ug. per ml. almost always had megaloblastic anaemia or obvious morphological changes of folate deficiency. In patients with borderline serum folate levels (3 0-5 9 m,tg. per ml.) haematological changes varied widely. The degree of change correlated with the red cell folate level in these patients.The formiminoglutamic acid (Figlu) test was positive (range 20-660 mg. excreted in eight hours) in all 30 patients with megaloblastic anaemia due to folate deficiency tested and also in 17 (31 %) of 54 non-anaemic patients who were folate deficient. The amount of Figlu excreted paralleled the red cell folate level in both the anaemic and non-anaemic, folate-deficient patients tested. Figlu excretion, like the red cell folate level, appeared to be a satisfactory index of tissue folate stores.In 46 patients with pernicious anaemia, the red cell folate levels ranged from 26 to 396 mp,g. per ml., 29 (63 %) of them having subnormal ...

Serum and red blood cell folate levels in parturients, in the intervillous space of the placenta and in full-term newborns

“…The fact that the levels of red blood cell folates in the intervillous space of the placenta were, on the average, almost identical to those in the mother and the fact that the correlation coefficient between them was close to one indicate that the erythrocytes suffer no alterations in terms of their folate stores when circulating in the intervillous space of the placenta. Positive correlation has been reported between serum and red blood cell folate concentrations [2,3,5,7] and the results obtained in the present paper confirm these observations. Thus, the correlation existing between the red blood cell folate levels in mothers and newborns may simply be the consequence of the correlation between serum folate levels in the mother-newborn binomium.…”

Folate intakes and folate biomarker profiles of pregnant Japanese women in the first trimester

“…The optical density of each well was measured using a single wavelength of 570 nm. RBC folate level was then calculated from the mean whole-blood folate value by subtracting folate content of serum in the sample, and corrected by hematocrit value (Hoffbrand et al, 1966).…”

Folate state of premature infants.

“…The normal adult levels of red cell folate were considered by Hoffbrand, Newcombe, and Mollin (1966) to lie between 160 and 640 ng./ml. of packed red cells.…”