Direct microtitre plate enzyme immunoassay of folic acid without heat denaturation of serum

Abstract

A new and simple method for enzyme immunoassay of folic acid (FA) has been developed, which does not require extraction or heat denaturation of serum. FA-free serum for standards was prepared by a new immunosorbent technique as conventional methods were unsuccessful. The detection limit of the assay is 0.05 ng/ml. Intra- and interassay variabilities ranged between 5–13.3%. Analytical recoveries obtained after spiking with different amounts of FA ranged between 93–110%. We eliminated the interference of endogenous folate binding protein — a major problem in direct FA assay by incubating serum samples (or standards) with FA-HRP conjugate in antibody coated plates at 50°C. Comparison of our data with results obtained by microbiological assay and also by heating samples in alkaline buffer showed good correlation.