Measurement of Red Cell Folate Levels by 3H‐Pteroylglutamic Acid (3H‐PteGlu) Radioassay

Summary. A siniple, rapid radioassay is described for the determination of red cell folate activity utilizing commercially available beta lactoglobulin as thc folate binding protein. The standard curve is prepared with a pteroylpolyglutamate and 3H‐pteroylglutamic acid. The test is performed with a maximum of 20 nicrolitres of whole blood and multiple samples can be processed within 1 hr. Values of red cell folate in normal subjects range from 200 to 875 ng/ml packed cells giving good correlation with established microbiological procedures. Red cell folate levels were lowest in patients whose folate deficiency was accompanied by anaemia. This assay may be useful for measurement of pteroylpolyglutamates in other tissues since an equimolar amount of N‐5‐methyl tetrahydrofolate is barely measurable under the conditions of this assay.