Radioassay of serum folate with use of pig plasma folate binders.

Pig plasma has been used as a source of specific folate binders for the development of a rapid radioassay to measure the concentration of folate in serum. The assay uses 3H-pteroylglutamic acid as tracer and N-5-methyltetrahydrofolic acid for the construction of the standard curve. The assay is run in a two-step incubation system of 15 min each at room temperature. Comparison between the results obtained with this method and a microbiological one indicated that for sera with relatively high folate levels there was a good agreement between the two methods, whereas for sera with low folate levels the present method produces lower values than the microbiological one. The diagnostic value of the results obtained by the two methods is discussed on the basis of the availability to the tissues of the folates which are firmly bound to specific folate binders of human serum.