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).